Case Information
*4
BERZON, Circuit Judge:
We once again consider the application of the Fourth
Amendment’s warrant requirement to new forms of
communication technology.
See, e.g.
,
United States v. Cano
,
934 F.3d 1002 (9th Cir. 2019);
cf. Carpenter v. United
States
, 138 S. Ct. 2206 (2018). “When confronting [such]
concerns wrought by digital technology, th[e] [Supreme]
Court [and this court] ha[ve] been careful not to uncritically
extend existing precedents.”
Id.
at 2222. Our question this
time concerns the private search exception to the Fourth
Amendment—specifically,
the
intersection between
electronic communications providers’ control over material
on their own servers and the Fourth Amendment’s restriction
of warrantless searches and seizures, which limits only
governmental action.
See Burdeau v. McDowell
, 256 U.S.
465 (1921);
Walter v. United States
,
The events giving rise to Luke Wilson’s conviction and this appeal were triggered when Google, as required by federal law, reported to the National Center for Missing and Exploited Children (NCMEC) that Wilson had uploaded four images of apparent child pornography to his email account as email attachments. No one at Google had opened or viewed Wilson’s email attachments; its report was based on an automated assessment that the images Wilson uploaded were the same as images other Google employees had earlier viewed and classified as child pornography. Someone at NCMEC then, also without opening or viewing them, sent Wilson’s email attachments to the San Diego Internet Crimes Against Children Task Force (ICAC), where an officer ultimately viewed the email attachments without a warrant. The officer then applied for warrants to search *5 6 U NITED S TATES V . W ILSON both Wilson’s email account and Wilson’s home, describing the attachments in detail in the application.
Our question is whether the government’s warrantless
search of Wilson’s email attachments was justified by the
private search exception to the Fourth Amendment.
See
Walter
,
I. Background
A. Google’s Identification of Apparent Child Pornography
Electronic communication service providers are not required “affirmatively [to] search, screen, or scan” for apparent violations on their platforms of federal child pornography laws. 18 U.S.C. §§ 2258A(f), 2258E. But “[i]n order to reduce . . . and . . . prevent the online sexual exploitation of children,” such providers, including Google, are directed, “as soon as reasonably possible after obtaining actual knowledge” of “any facts or circumstances from which there is an apparent violation of . . . child pornography [statutes],” to “mak[e] a report of such facts or circumstances” to NCMEC. 18 U.S.C. § 2258A(a). [1] NCMEC then forwards what is known as a CyberTip to the [1] “A provider that knowingly and willfully failed to make a report required . . . shall be fined.” 18 U.S.C. § 2258A(e). Further, in the case of “intentional, reckless, or other misconduct,” there may be “a civil claim or criminal charge against a provider . . . arising from the performance of the reporting or preservation responsibilities.” Id . at §§ 2258B(a), (b).
appropriate law enforcement agency for possible investigation. Id. at §§ 2258A(a)(1)(B)(ii), (c).
According to a two-page declaration from a senior manager at Google, the company “independently and voluntarily take[s] steps to monitor and safeguard [its] platform,” including using a “proprietary hashing technology” to identify apparent child pornography.
As described in the record—vaguely, and with the gaps noted—the process works as follows:
First, a team of Google employees are “trained by counsel on the federal statutory definition of child pornography and how to recognize it.” Neither the training materials themselves nor a description of their contents appear in or are attached to the Google manager’s declaration.
Second, these employees “visually confirm[]” an image “to be apparent child pornography.” According to an industry classification standard created by various electronic service providers, there are four industry categorizations: “A1” for a sex act involving a prepubescent minor; “A2” for a lascivious exhibition involving a prepubescent minor; “B1” for a sex act involving a pubescent minor; and “B2” for a lascivious exhibition involving a pubescent minor.
Third, “[e]ach offending image” judged to be “apparent child pornography as defined in 18 USC § 2256” is given a hash value, which is “added to [the] repository of hashes.” *7 attachments. According to the Google manager’s declaration, “a Google employee did not view the images . . . concurrently to submitting the report to NCMEC.” The CyberTipline report did specify that Google had classified each of Wilson’s four email attachments as “A1” under an industry classification standard for “content [which] contain[s] a depiction of a prepubescent minor engaged in a sexual act.”
Google’s report included Wilson’s email address, secondary email address, and IP addresses. NCMEC supplemented Google’s report with geolocation information associated with Wilson’s IP addresses, but did “not open[] or view[] any uploaded files submitted with this report.”
NCMEC then forwarded the CyberTip to the San Diego Internet Crimes Against Children Task Force (“ICAC”). Agent Thompson, a member of the San Diego ICAC, received the report. He followed San Diego ICAC procedure, which at the time called for inspecting the images without a warrant whether or not a Google employee had reviewed them. [3]
After Agent Thompson looked at Wilson’s four email attachments, he applied for a search warrant of Wilson’s email account. His affidavit asserted that probable cause for the warrant was based on two facts: first, that “Google became aware of four (4) image files depicting suspected child pornography;” and second, that he had “reviewed the four (4) images reported by Google to NCMEC and determined they depict child pornography.” In support of his own child pornography assessment, he included in the warrant application detailed “descriptions of each of these images.” The affidavit did not include the fact that Google had originally classified the images as “A1” or provide any detail about how Google had either classified or later automatically identified Wilson’s images as apparent child pornography.
On the basis of the application and affidavit submitted by Agent Thompson, a magistrate judge issued a search Agent Thompson testified that San Diego ICAC, which includes both local, county, regional, and federal agencies, now obtains a search warrant before opening a CyberTip when the provider has not viewed the images. It is not clear from the record whether other ICAC task forces across the country have adopted the same policy.
10 U NITED S TATES V . W ILSON warrant for Wilson’s email account. When Agent Thompson executed the warrant, he discovered numerous email exchanges in which Wilson received and sent images and video files of alleged child pornography and in which Wilson offered to pay for the creation of child pornography.
Agent Thompson then obtained a search warrant for Wilson’s residence. On executing the warrant, law enforcement officers found and seized several electronic devices that contained evidence of child pornography. One officer observed a backpack being tossed over Wilson’s balcony at the time officers were knocking on Wilson’s door and announcing their presence. Wilson’s checkbook and a thumb drive containing thousands of images of child pornography—including the four images reported by Google—were found in the backpack.
C. Motion to Suppress
Wilson filed a motion to suppress all evidence seized
from his email account and residence, arguing that Agent
Thompson’s review of his email attachments without a
warrant was impermissible under the Fourth Amendment.
Relying principally on ,
The district court agreed. The court denied Wilson’s motion to suppress on the ground that the government’s warrantless search did not exceed the scope of the antecedent private search and so did not require a warrant. The district court also concluded that “if [Agent] Thompson’s *9 warrantless viewing of the four images constituted an illegal search, neither excising the tainted evidence from the affidavit nor the good faith exception would prevent operation of the exclusionary rule.” [4] Wilson , 2017 WL 2733879, at *12–13.
After waiving his right to a jury trial, Wilson was
convicted of possession and distribution of child
pornography
[5]
and sentenced to 11 years of incarceration and
[4]
The government does not contest these contingent rulings.
*10
United States v. Miller
,
exception, such that the Fourth Amendment did not require him to procure a warrant.
We review the district court’s denial of Wilson’s motion
to suppress
de novo
and the district court’s underlying
factual findings for clear error.
See United States v. Camou
,
A. Private Search Exception
As the Fourth Amendment protects individuals from
government actors, not private ones,
see Burdeau v.
McDowell
,
1. Doctrinal Foundations
Beginning from the initial articulation of the private
search doctrine, the extent to which it excuses the
government from compliance with the warrant requirement
of the Fourth Amendment has been the subject of concern.
The exception has, for example, been described as
“unsettling” for its potential reach. 1 Wayne R. LaFave,
Search and Seizure: A Treatise on the Fourth Amendment
§1.8(b) (6th ed. 2020);
see also Jacobsen
,
Beginning with
Burdeau
, the Supreme Court has
distinguished between government agents and private
parties for purposes of the Fourth Amendment.
Burdeau
considered whether the Fourth Amendment restricts the
government’s ability to use papers incriminating an
individual when those papers were volunteered to the
government by a private party who had stolen them.
Burdeau
disregarded the private theft, noting that although “[t]he
Fourth Amendment gives protection against unlawful
searches and seizures, . . . its protection applies to
governmental action.”
Coolidge
, decided 50 years after
Burdeau
, addressed
whether a private party who provides the government with
another person’s contraband or evidentiary material can be
considered an agent of the government for purposes of the
Fourth Amendment. In that case, local police officers arrived
at a suspect’s home, questioned his wife about his
involvement in a murder, and obtained from his wife a rifle
and articles of clothing belonging to the suspect.
Coolidge
,
U NITED S TATES V . W ILSON 15 evidence.” Id . at 487. The relevant inquiry, according to the Court, was whether the suspect’s wife, “in light of all the circumstances of the case, must be regarded as having acted as an instrument or agent of the state when she produced her husband’s belongings.” Id. (internal quotation marks omitted). As the record showed that the suspect’s wife had shared the suspect’s guns and clothes with the local police “of her own accord,” Coolidge held that “it was not incumbent on the police to stop her or avert their eyes” when offered the critical evidence. Id . at 489.
2. Doctrinal Scope
Following
Burdeau
and
Coolidge
, both
Walter
and
Jacobsen
considered a warrantless government search after
a private party “freely made available” certain information
for the government’s inspection. ,
In Walter , a package of obscene films was mistakenly delivered to the wrong recipient. 447 U.S. at 651. The recipient opened the external packaging and examined the boxes containing individual films. Id. at 651–52. Each box displayed “suggestive drawings” on one side and “explicit descriptions of the contents” of the film on the other. Id. at 652. After reading these descriptions, and “attempt[ing] without success to view portions of the film by holding it up to the light,” the recipient notified the FBI about the mistaken delivery. Id . The FBI then seized the boxes and screened one of the films without first obtaining a warrant. Id .
Walter did not result in a majority opinion, but a majority of the justices concluded that there had been a violation of *13 the Fourth Amendment, and a different majority of justices agreed on the standard to be applied.
Justice Stevens, joined by Justice Stewart, announced the judgment of the Court. Their opinion concluded that the government search exceeded the scope of the antecedent actions by the private individuals in two respects. First, the government agents had screened the film for the purpose of learning information necessary to determine that a crime had been committed:
It is perfectly obvious that the agents’ reason for viewing the films was to determine whether their owner was guilty of a federal offense. To be sure, the labels on the film boxes gave them probable cause to believe that the films were obscene and that their shipment in interstate commerce had offended the federal criminal code. . . . [But] a search of the contents of the films . . . was necessary in order to obtain the evidence which was to be used at trial.
Id . at 654. Second, the government agents had gone beyond the physical bounds of the private search, because “the private party had not actually viewed the films.” Id . at 657. “The private search [thus] merely frustrated [the] expectation [of privacy] in part,” not in full. Id . at 659. “It . did not simply strip the remaining unfrustrated portion of that expectation of all Fourth Amendment protection.” Id [8]
The four justices in dissent would have concluded that there was no Fourth Amendment violation. The dissenters disputed not the basic approach of Justice Stevens’ opinion but its application to the facts of the case. Specifically, the dissent stressed that “[t]he containers . . . clearly revealed the nature of their contents,” such that the private employees “so fully ascertained the nature of the films . . . [that] the FBI’s subsequent viewing of the movies . . . was not an additional search subject to the warrant requirement.” Id . at 663–64 (Blackmun, J., dissenting, joined by Burger, C.J., and Powell and Rehnquist, JJ.).
Four years after
Walter
, the Supreme Court again applied
the private search doctrine. Importantly,
Jacobsen
recognized “the agreement [in
Walter
] on the standard to be
*14
applied in evaluating the relationship between the two
searches.”
Jacobsen
concerned a government search of a Federal
Express (“FedEx”) package that had been partially opened
by FedEx employees.
See
package,” “cut open the tube” within the package, and “found a series of four zip-lock plastic bags, the outermost enclosing the other three and the innermost containing about six and a half ounces of white powder.” Id . The employees “observed . . . white powder in the innermost plastic bag,” but did not open the (presumably transparent) bag. Id . Instead, they called the Drug Enforcement Administration (DEA), put the plastic bags back in the tube, and placed the tube back in the box. Id .
When DEA agents arrived, they did two things: First, to visually inspect the contents of the plastic bags, DEA agents removed the tube from the box and the plastic bags from the tube. See id. Second, federal agents “opened each of the four bags and removed a trace of the white substance with a knife blade.” Id . at 111–12. They performed a field test to determine whether the powder in the plastic bags was cocaine. See id .
Jacobsen
considered whether the private search
exception as adopted by a majority of justices in
Walter
applied to the facts at hand. In doing so, , like
Justice Stevens’ opinion in
Walter
, looked at both the degree
to which the government’s actions led to observing new
information not uncovered by the private search and the
extent to which the government’s investigation intruded on
the package owner’s privacy interests to a greater degree
than had the private party’s actions. As to the first parameter,
the information gleaned by the government,
Jacobsen
permitted the government agent to “reexamine”—that is,
examine in the same manner—the package previously
*15
examined by FedEx, the private party. The government
“could utilize the [private] employees’ testimony concerning
the contents of the package,” noted ; “[p]rotecting
the risk of misdescription . . . is not protected by the Fourth
Amendment.”
Applying these precepts, Jacobsen concluded that the “removal of the plastic bags from the tube and the [government] agent’s visual inspection of their contents” did not exceed the scope of the private search as to the information obtained. Id. at 120. “[T]he agent[s] . . . learn[ed] nothing [from those actions] that had not previously been learned during the private search” and conveyed to the federal agents by the FedEx employees. Id . And as to the privacy interests, the governmental search to that point “infringed no legitimate expectation of privacy and hence was not a ‘search’ within the meaning of the Fourth Amendment,” id ., as “[t]he package itself, which had previously been opened, remained unsealed, and the Federal Express employees had invited the agents to examine its contents,” such that “the package could no longer support any expectation of privacy,” id . at 121.
Jacobsen
then separately considered the chemical field
test, conducted by the DEA agents, including the federal
agents’ removal of the white powder from the plastic bag.
Critically for our purposes,
Jacobsen
began this inquiry from
the premise that because the field test “had not been
conducted by the Federal Express agents,” it “
therefore
exceeded the scope of the private search.”
Id
. at 122
(emphasis added). The majority then determined that the
government’s chemical field test of the substance in the
properly seized plastic bags was nonetheless not a search
*16
20
U NITED S TATES V . W ILSON within the meaning of the Fourth Amendment, because
“governmental conduct that can reveal whether a substance
is cocaine, and no other arguably ‘private’ fact, compromises
no legitimate privacy interest.”
Id
. at 122–23. This
conclusion,
Jacobsen
explained, was “dictated” by the
Court’s earlier decision in
United States v. Place
, 462 U.S.
696 (1983), “in which the Court held that subjecting luggage
to a ‘sniff test’ by a trained narcotics detection dog was not
a ‘search’ within the meaning of the Fourth Amendment.”
Jacobsen
,
B. Application of the Private Search Exception to This Case
The government bears the burden to prove Agent
Thompson’s warrantless search was justified by the private
search exception to the Fourth Amendment’s warrant
requirement. Before considering
the private search
exception,
Coolidge
emphasized “the most basic
constitutional rule” in the Fourth Amendment arena:
warrantless searches are per se unreasonable, subject to few
exceptions that are “jealously and carefully drawn.”
Both as to the information the government obtained and
the additional privacy interests implicated, the government’s
actions here exceed the limits of the private search exception
as delineated in
Walter
and and their progeny.
[9]
Wilson opines that the private search exception to the Fourth
Amendment should be overruled, and seeks to preserve that question for
any Supreme Court review of this case. As a court of appeals, we of
First, the government search exceeded the scope of the
antecedent private search because it allowed the government
to learn new, critical information that it used first to obtain a
warrant and then to prosecute Wilson. Second, the
government search also expanded the scope of the
antecedent private search because the government agent
viewed Wilson’s email attachments even though no Google
employee—or other person—had done so,
thereby
*17
course cannot overrule Supreme Court cases.
United States v. Weiland
,
1. Additional Information The district court analogized Agent Thompson’s review of Wilson’s email attachments to the government search in , concluding that Agent Thompson’s search allowed him to “learn nothing new,” because Google had already classified the images as child pornography. Wilson , 2017 WL 2733879, at *10–11. The government similarly argues on appeal that its official search did not impermissibly expand the scope of the private search because it “just confirmed what Google employees already knew and could say.” Both the district court’s conclusion and the governments’ argument misstate the record.
The record indicates that Google does not keep a repository of child pornography images, so no Google employee could have shown the government the images it believed to match Wilson’s. Nor does the record identify the individual who viewed those images in the repository, so no identified Google employee “knew and could say” what those images showed. Instead, Google keeps a repository of unique hash values corresponding to illicit images, and tags each image with one of four generic labels. All Google communicated to NCMEC in its CyberTip was that the four images Wilson uploaded to his email account matched images previously identified by some Google employee at some time in the past as child pornography and classified as depicting a sex act involving a prepubescent minor (the “A1” classification). [10] Based only on the barebones CyberTip, Agent Thompson testified, he opened and reviewed each of Wilson’s images to determine “whether or not it is a case that . . . can be investigated” for violations of federal law.
A detailed description of the images was then included in the applications for search warrants. The gulf between what Agent Thompson knew about Wilson’s images from the CyberTip and what he subsequently learned is apparent from those descriptions. In contrast to Google’s label of the images just as “A1,” which the government did not mention in the warrant application, the government learned the following:
1. 140005125216.jpg – This image depicts a young nude girl, approximately five (5) to nine (9) years of age, who is lying on her stomach with her face in the nude genital region of an older female who is seated with her legs spread. A second young girl, approximately five (5) to nine (9) years of age, is also visible in this image and she is partially nude with her vagina exposed. Google identified this image was uploaded on June 4, 2015, at 16:11:04 UTC.
2. 140005183260.jpg – This image depicts a young nude girl, approximately five (5) to nine (9) years of age, who is lying on top of Perhaps a Google employee could also have testified to details about the company’s proprietary technology. But no such information appears in the record, and the CyberTip did not convey any more information than what is now included in the record.
24 U NITED S TATES V . W ILSON an older nude female, approximately eighteen years of age. Within this image the girl’s genital regions are pressed against one another and the older girl appears to be touching the face of the younger child with her tongue. Google identified this image was uploaded on June 4, 2015, at 16:11:21 UTC. 3. 140005129034.jpg – This image depicts a partially nude young girl, approximately five (5) to nine (9) years of age, who is lying on her back with her legs spread and her vagina exposed. An older female is positioned in front of this girl’s exposed vagina in this image and the younger girl has her left hand on the vaginal/buttocks area of a second nude girl of similar age. Google identified this image was uploaded on June 4, 2015, at 16:11:06 UTC.
4. 1400052000787.jpg – This image depicts a wider angle view of the previously referenced images possessing file names 140005125216.jpg and 140005129034.jpg as reported by Google.
Wilson
,
Given the large gap between the information in the
CyberTip and the information the government obtained and
used to support the warrant application and to prosecute
Wilson, the government search in
Walter
offers a much more
apt comparison to the circumstances here than does the
government search in . Google’s categorization of
Wilson’s email attachments as “A1” functioned as a label for
*20
the images in the same way that the boxes describing the
films in
Walter
suggested that the images on the films were
obscene. The “A1” labels, in fact, provided less information
about the images’ contents than did the boxes in
Walter
,
which had “explicit descriptions of the contents” of the film.
Viewing Wilson’s email attachments—like viewing the
movie in
Walter
—substantively expanded the information
available to law enforcement far beyond what the label alone
conveyed, and was used to provide probable cause to search
further and to prosecute. The government learned at least
two things above and beyond the information conveyed by
the CyberTip by viewing Wilson’s images: First, Agent
Thompson learned exactly what the image showed. Second,
Agent Thompson learned the image was in fact child
pornography. Until he viewed the images, they were at most
“suspected” child pornography. Just as it “was clearly
necessary for the FBI to screen the films [in
Walter
], which
the private party had not done, in order to obtain the evidence
needed to accomplish its law enforcement objectives,”
Walter
,
Importantly, the district court found—and we agree—
that if Agent Thompson’s affidavit in support of a warrant
had been “excise[d]” of “the tainted evidence,” “the affidavit
would not support issuance of the search warrant for
Defendant’s email account.”
Wilson
, 2017 WL 2733879,
at *12. The district court’s findings about the inadequacy
of the warrant application without the important information
Agent Thompson obtained by viewing Wilson’s images
demonstrate that the government learned new, critical
information by viewing Wilson’s images, information “not
previously . . . learned during the private search,” ,
2. Additional Intrusion on Wilson’s Privacy Interest
The government also maintains that directly viewing Wilson’s images for the first time was not a further invasion of Wilson’s privacy, beyond any privacy invasion by Google. The government’s expectation of privacy analysis fails for much the same reason as did its argument that it learned nothing new by viewing the images.
The government’s central submission in this regard is
that Wilson’s expectation of privacy in his images was fully
frustrated when Google’s computer technology scanned
them, such that any further government search of the images
[11]
We also agree with the district court that the government might
have been able to demonstrate probable cause sufficient to obtain a
warrant without the descriptions of Wilson’s images, by presenting, for
example, more “information about Google’s screening process for child
pornography,”
Wilson
,
should be exempt from the Fourth Amendment’s warrant requirement. We cannot agree.
Although Google’s proprietary technology labelled
Wilson’s email attachments as “A1,” “the content of the
[images] . . . was [no more] apparent” to Google than the
image content was to the private party in
Walter
, as no
Google employee had opened and viewed the attachments,
and Google does not appear to retain any record of the
original images used to generate hash matches.
See Tosti
,
The government’s argument to the contrary mischaracterizes the record, by representing that Google’s scan “ equates to a full-color, high-definition view” of Wilson’s images. It does not. The critical fact is that no Google employee viewed Wilson ’s files before Agent The government stated at oral argument that it is not relying on the contraband nature of child pornography as a justification for the search. .
Thompson did. When the government views anything other
than the specific materials that a private party saw during the
course of a private search, the government search exceeds
the scope of the private search. That is the clear holding of
Jacobsen
. In that case, “[t]he field test . . . had not been
conducted by the Federal Express agents and
therefore
exceeded the scope of the private search
.”
3. Personal Nature of the Fourth Amendment
The government attempts to save its warrantless search
by shifting the analysis from the private search of Wilson’s
files, flagged by Google and classified as A1 by its
proprietary technology, to the private search of other
individuals’ files, which some Google employee previously
viewed and classified as child pornography in Google’s
database of hash values. The government argues that Agent
Thompson’s search did not exceed the bounds of the private
search because a Google employee had previously viewed
different child pornography files, and Google’s computers
flagged Wilson’s email attachments as containing the same
images as those files, using an unspecified hash value
comparison system. This line of argument cannot save the
validity of the government’s search. Even if Wilson’s email
attachments were precise duplicates of different files a
Google employee had earlier reviewed and categorized as
child pornography, both
Walter
and
Jacobsen
—and general
Fourth Amendment principles—instruct that we must
specifically focus on the extent of Google’s private search of
Wilson’s
effects, not of other individuals’ belongings, to
assess whether “the additional invasions of [Wilson’s]
privacy by the government agent . . . exceeded the scope of
the private search.” ,
U NITED S TATES V . W ILSON 29 To see why, consider whether Walter would have come out differently had the misdirected package come into the hands of someone who had previously viewed another copy of the same film and, recognizing the box, told the police that the film in it was, in her view, legally obscene. Under Walter , the government in the hypothesized circumstance would still need a warrant to view the film in the box. Viewing the copy of the film actually in the box, which the mistaken recipient of the box had not done, would still entail an additional governmental intrusion on both the physical integrity of the film and the owner’s privacy interest in its content.
Fourth Amendment rights are
personal
rights.
Rakas v.
Illinois
,
So Wilson did not have an expectation of privacy in other individuals’ files, even if their files were identical to his files. The corollary of this principle must also be true: Wilson did have an expectation of privacy in his files, even if others had identical files. If, for example, police officers search someone else’s house and find documents evidencing wrongdoing along with notes indicating that I have identical documents in my house, they cannot, without a warrant or some distinct exception to the warrant requirement, seize my copies. I would retain a personal expectation of privacy in them, and in my connection to them, even if law enforcement had a strong basis for anticipating what my copies would contain. A violation of a third party’s privacy has no bearing on my reasonable expectation of privacy in my own documents. The government does not argue otherwise.
In short, whether Google had previously reviewed, at
*24
some earlier time,
other individuals’
files is not pertinent to
whether a private search eroded
Wilson’s
expectation of
privacy. Under the private search doctrine, the Fourth
Amendment remains implicated “if the authorities use
information with respect to which the expectation of privacy
has
not
already been frustrated.”
Jacobsen
,
C. Relevant Appellate Caselaw (i) Our application of Jacobsen and Walter is consistent with Ninth Circuit case law. The district court misapplied United States v. Tosti , 733 F.3d 816 (9th Cir. 2013), in reaching the contrary conclusion.
In Tosti , a private party entrusted with the defendant’s computer found thumbnails of images believed to be child pornography and alerted law enforcement officers. 733 F.3d at 818–19. The private party showed the thumbnails to law enforcement, and the agents “could tell from viewing the thumbnails that the images contained child pornography.” Id . at 822.
Tosti
held that law enforcement’s enlarging of the
thumbnails did not expand on the antecedent private search.
For one, based on the standard articulated in , “the
police learned nothing new through their actions.”
Tosti
,
Neither is true in this case. Here, what was conveyed to
Agent Thompson was that a not-yet-viewed image uploaded
by Wilson matched a different image that an unidentified
Google employee had previously viewed and classified as
child pornography. So until Agent Thompson actually
viewed the images, he knew only that Google’s propriety
technology had identified a match between Wilson’s images
and other images that Google had classified as child
pornography. He “learned . . . [a]new through [his] actions,”
for the first time, what the images actually showed.
See supra
pp. 23–24. And, as no one at Google had previously
viewed Wilson’s attachments, “any privacy interest in those
images had [not] been extinguished.”
Tosti
,
For these reasons, Tosti is fully consistent with our conclusion that Agent Thompson’s search exceeded the scope of the private search and so required a warrant.
(ii) In so holding, we contribute to a growing tension in the circuits about the application of the private search doctrine to the detection of child pornography.
In
United States v. Ackerman
,
Ackerman did suggest that, had the government viewed only the attachment AOL identified as a hash value match and not other attachments and the text of the defendant’s email, that distinction might “bring the government closer to a successful invocation of the private search doctrine.” Id. at 1308 (emphasis added). But Ackerman also noted that in that circumstance—which appears to be what happened here—the government’s action may still be a new search, as the government, “might . . . have risked exposing new and protected information, maybe because the hash value match could have proven mistaken . . . or because the AOL employee who identified the original image as child pornography was mistaken in his assessment.” Id. at 1306. Although Ackerman did not decide the precise issue before us, and expressly disavowed “prejudg[ing]” it, id . at 1308– 09, its underlying analysis is entirely consistent with ours, and its suggestions about why there could be a search in our circumstances echo some of the reasons we have given for so concluding.
Other private search cases concerning the discovery of
child pornography, outside the context of automated hash
value matching, have also ruled consistently with our
*26
understanding of the limited scope of the private search
exception. For example, in
United States v. Lichtenberger
,
Further, in
United States v. Sparks
,
Both the Fifth Circuit and the Seventh Circuit have held that an
individual’s privacy interest in a digital container, such as an email
account, cell phone, or laptop, is entirely frustrated whenever any part of
the container is searched.
See United States v. Runyan
,
The Fifth Circuit held the private search exception
justified the government’s warrantless search because the
government agent’s “visual review of the suspect images . . .
the scope of digital information, and is inconsistent with
Jacobsen
. For
starters,
Tosti
did not regard the viewing of some files as sufficient for
purposes of the private search doctrine to show that the government only
invaded a defendant’s privacy interests to the same extent as the private
party.
See
was akin to the government agents’ decision to conduct chemical tests on the white powder in Jacobsen ,” insofar as “opening the file merely confirmed that the flagged file was indeed child pornography, as suspected.” Reddick , 900 F.3d at 639.
We cannot accept this analysis for several reasons. First, and most important, Reddick conflates ’s first *28 holding regarding the private search exception to the Fourth Amendment with its second holding regarding whether the field test constituted a search under the Fourth Amendment. The private search exception excuses a warrantless government search that would otherwise violate the Fourth Amendment; the field test determination in Jacobsen , based on Fourth Amendment law outside the private search context, was that a warrantless government field drug test simply does not trigger the Fourth Amendment’s protections. 466 U.S. at 123–24. In other words, the warrantless chemical test in Jacobsen was not excused via the private search exception but for an entirely different reason—that confirming through a field test that an already exposed and seized contraband substance was a drug is not a search for Fourth Amendment purposes. Id . at 122.
Moreover, in Jacobsen , the white powder was fully visible to the government officers when they repeated the steps taken by the FedEx employees to inspect the package. Not so here, as no human had viewed Wilson’s images before. The part of that does elucidate the private search doctrine cannot govern here.
Notably, we have held that the chemical field test exception to the Fourth Amendment’s warrant requirement does not apply to a more complete chemical analysis of a drug. In United States v. Mulder , 808 F.2d 1346 (9th Cir. 1987), a hotel security officer removed items left behind in a hotel room after a guest’s scheduled departure, including plastic bags full of tablets, and provided them to federal agents. Id. at 1347. The tablets “were tested at the Western Regional Laboratory through the use of mass spectrometry, infrared spectroscopy and gas chromatography.” Id . at 1348. Mulder distinguished between the chemical field test in Jacobsen and a laboratory test: “[T]he chemical testing in this case was not a field test which could merely disclose whether or not the substance was a particular substance, but was a series of tests designed to reveal the molecular structure of a substance and indicate precisely what it is. Because of the greater sophistication of these tests, they could have revealed an arguably private fact,” and thus compromised the defendant’s legitimate privacy interest. Id . at 1348–49.
To the extent opening an email attachment to view its
contents is analogous to drug testing at all, it is akin to a
laboratory
test with the potential to reveal new private
information, as in
Mulder
, not a binary field test that yields
either a positive or negative result. Just as a laboratory test
of a suspected drug reveals its precise molecular structure
*29
and so potentially exposes additional private information
like other illicit contaminants or the source of the substance,
so viewing an image of suspected child pornography reveals
innumerable granular private details—for example, the faces
of the people depicted, the setting, and, perhaps, other
speech or conduct also in the frame. Viewing the images
here allowed the government to do more than just confirm
the images’ classification as child pornography, implicating
privacy interests beyond a binary classification. Contrary to
Reddick
, the government’s “
visual
review of the suspect
images” was not analogous to “the government agents’
decision to conduct chemical tests on the white powder in
.”
Miller instead resolved the Fourth Amendment question it faced by focusing exclusively on the assumed reliability of Google’s proprietary technology. “At bottom,” Miller explained, “this case turns on the question whether Google’s hash-value matching is sufficiently reliable.” Id. at 429–30. Because the defendant in Miller “never challenged the reliability of hashing,” id . at 430 (internal brackets and quotation omitted) ( Miller thought the burden was on the defendant, see id. at 430), Miller deferred to the district court’s finding “that the technology was ‘highly reliable.’” Id.
Wilson, by contrast, did challenge the “accuracy and reliability” of Google’s hashing technology in the district court. And, contrary to Miller ’s assertion, the government bears the burden to prove its warrantless search was permissible, see supra p. 20—a burden it failed to carry.
Our analysis, however, relies only contingently on the adequacy of the record with regard to the hash match technology. In our view, the critical factors in the private search analysis, both unacknowledged in Miller , include the personal nature of Fourth Amendment rights and the breadth of essential information Agent Thompson obtained by opening the attachment, information—and a privacy invasion—well beyond what Google communicated to NCMEC. See supra Parts II.B.1, II.B.2. The reliability of *30 Google’s proprietary technology, in our estimation, is 38 U NITED S TATES V . W ILSON pertinent to whether probable cause could be shown to obtain a warrant, not to whether the private search doctrine precludes the need for the warrant.
And, as the district court noted, and we have noted as well, the warrant application here contained inadequate information about Google’s proprietary technology to establish probable cause without reliance on the descriptions of the actual images. See supra p. 25.
III. Conclusion
“When confronting new concerns wrought by digital
technology, this Court has been careful not to uncritically
extend existing precedents.”
Carpenter
,
Having examined this case with the requisite care, we hold, for the reasons explained, that Agent Thompson violated Wilson’s Fourth Amendment right to be free from unreasonable searches when he examined Wilson’s email attachments without a warrant. Wilson’s conviction is vacated, the district court’s denial of Wilson’s motion to *31 suppress is reversed, and this case is remanded for further proceedings. [14]
As noted, the district court concluded that if Agent Thompson’s
warrantless actions constituted an illegal search, no exception “would
prevent operation of the exclusionary rule.”
Wilson
,
Notes
[2]
“A hash value is (usually) a short string of characters generated
from a much larger string of data (say, an electronic image) using an
algorithm.”
United States v. Ackerman
,
[5]
While this appeal was pending, the California Court of Appeal held
that “the government’s warrantless search of Wilson’s four images was
permissible under the private search doctrine.”
People v. Wilson
, 56 Cal.
App. 5th 128, 147 (2020),
as modified on denial of reh’g
(Nov. 6, 2020),
review denied (
Jan. 20, 2021). We have not squarely addressed the
preclusive effect of the denial of a suppression motion in an earlier state-
court proceeding. Other circuits, however, have held that “the
government may not collaterally estop a criminal defendant from
relitigating an issue against the defendant in a different court in a prior
proceeding.”
United States v. Harnage
, 976 F.2d 633, 636 (11th Cir.
1992);
accord United States v. Pelullo
,
[6] II. Discussion
The government does not dispute for purposes of this
case Wilson’s assertion that Agent Thompson’s review of
his email attachments was a search within the meaning of the
Fourth Amendment. We proceed on that assumption as
well—that is, we assume that Wilson had a subjective
expectation of privacy in his email attachments that society
is prepared to recognize as reasonable,
see Kyllo v. United
States
,