The government seeks to appeal the district court’s ruling suppressing drugs found in the back of Carlos Lopez’s truck, but failed to file in a timely manner the certification required by 18 U.S.C. § 3731 — that is, a document representing that its appeal is not taken for delay and the suppressed evidence is substantial proof of a fact material to the prosecution. Our precedent indicates, however, that this failure is not jurisdictional and should not preclude an appeal so long as the government has materially, if not formally, complied with Section 3731. Because the record demonstrates that the government did, in substance, undertake the evaluation called for by Section 3731 before noticing this appeal, we must proceed to its merits. Doing so, we hold that the events witnessed by government surveillance agents, taken as a whole, provided the officers reasonable suspicion to effect an investigative detention, and we therefore reverse.
I
A
On a December morning in 2006, Dana Suchma, a federal Drug Enforcement Agency special agent, conducted drug-interdiction surveillance at a Best Western hotel in Kansas City, Kansas, near an 1-35 interchange. Agent Suchma has ten years’ experience in this line of work, and has described his job as including surveillance in hotel/motel parking lots, with an eye toward locating cars that are from “source cities” and then gathering information about the car and driver from hotel employees or others before deciding whether the car’s journey sounds sufficiently suspicious to merit further monitoring for drug-related activity.
In the Best Western parking lot, Agent Suchma noticed a red pickup truck with its engine running and a person inside smoking a cigarette. Running a check on the truck’s Texas license plate, he discovered it was registered to a Carlos Lopez from Pharr, Texas. Agent Suchma consulted a map and found that Pharr is a suburb of McAllen, a border town in south Texas that he believed to be a source city where drugs are brought over the border. The agent then entered the hotel and learned from the clerk that Mr. Lopez checked in the night before at 10:38, checked out that morning at 9:01, and paid cash for his room.
Returning to his own car, Agent Suchma decided to continue monitoring the truck and requested assistance by radio from three other nearby members of his surveillance team. After nearly an hour idling in the hotel parking lot, Mr. Lopez moved his truck from the hotel parking space and drove to one of the parking spaces of a Sonic drive-in restaurant immediately adjacent to the hotel. The agents then saw a *793 green pickup truck, parked near Mr. Lopez’s truck in the Best Western parking lot, follow Mr. Lopez’s truck into the restaurant parking lot and pull into a space directly next to Mr. Lopez’s vehicle on the passenger side.
As soon as both pickup trucks arrived at the Sonic, the agents observed Mr. Lopez get out of his truck and walk to the front of it. At the same time, a passenger in the green truck, Alfonso Urena-Bonilla, exited that vehicle carrying a white styrofoam cooler, and, without speaking with Mr. Lopez, placed it in the bed of Mr. Lopez’s truck. While this transfer was occurring, the driver of the green truck, Ricardo Cardenas-Corona, got out and stood surveying the general area. Agent Suchma, concerned that the driver was engaged in counter-surveillance, relocated his vehicle to remain unnoticed.
Although Mr. Lopez and Mr. Cardenas-Corona stood outside their vehicles in parking spaces directly next to each other, the agents did not observe any communication between them. As soon as Mr. Urena-Bonilla deposited the cooler in Mr. Lopez’s truck, Mr. Lopez reentered the vehicle and backed out of the parking space, at which point Mr. Urena-Bonilla came over and spoke with him briefly. After this brief exchange, Mr. Lopez drove out of the Sonic parking lot and proceeded southbound on I-B5. None of the men apparently sought breakfast at the Sonic.
After following Mr. Lopez and observing him drive onto 1-35, Agent Suchma contacted a member of the Kansas Highway Patrol to request assistance in stopping Mr. Lopez’s truck. Highway Patrol Lieutenant Tom Catania and Trooper Charles Lovewell, in a car nearby, responded to the request by calling the agent on his cell phone. Agent Suchma told Lieutenant Catania what he and the other surveillance agents saw at the hotel and restaurant, gave a description of the truck and its plate number, and asked that the Lieutenant and his partner stop Mr. Lopez — for a traffic infraction if possible, although Agent Suchma believed he already had reasonable suspicion to justify an investigative stop.
Trooper Lovewell located Mr. Lopez’s truck and, after following him for a distance, observed the truck weave slightly and the right-side tires momentarily stray over the fog line. Believing this violated state law, Trooper Lovewell pulled Mr. Lopez over. After explaining why he stopped Mr. Lopez and examining his license, registration, and proof of insurance, Trooper Lovewell asked Mr. Lopez about his destination and the significant mileage on his relatively new truck. Mr. Lopez responded that he had driven from Florida to Dallas to Kansas City, and was now returning to Dallas, and that, although he had driven approximately 14,000 miles in the 4 months he had owned the truck, he did not use it for business. The troopers believed this amount of mileage likely excessive for leisure travel and consistent with the operations of a drug courier.
Trooper Lovewell issued Mr. Lopez a written warning for failing to maintain his lane of travel and returned his documents. After he told Mr. Lopez to “have a safe trip” and walked away from the vehicle, and after Mr. Lopez prepared to drive away, Trooper Lovewell turned back toward the truck and knocked on the window. Mr. Lopez motioned for him to open the passenger door, which he did. Trooper Lovewell then asked whether he could ask Mr. Lopez some additional questions. When Mr. Lopez did not object, Trooper Lovewell asked whether he had anything illegal in the vehicle, such as drugs. Lieutenant Catania also came alongside the truck and asked whether Mr. Lopez had any weapons or large amounts of currency. *794 Mr. Lopez responded “no” to these questions. Trooper Lovewell then asked if he could search the truck and Mr. Lopez answered affirmatively. Trooper Lovewell confirmed that Mr. Lopez understood his request to search and Mr. Lopez against consented. Opening the cooler in the truck bed revealed 3.3 kilograms of methamphetamine.
B
The government filed an indictment charging Mr. Lopez, along with Mr. Ure-na-Bonilla, with possession with intent to distribute 500 grams or more of methamphetamine, in violation of 21 U.S.C. § 841(a)(1) and (b)(1)(A). Mr. Lopez moved to suppress the contents of the cooler, alleging that his stop and search violated the Fourth Amendment. The district court agreed that the stop wasn’t based on reasonable suspicion of a legitimate traffic infraction. A single instance of straying across the fog line without some evidence that it was unsafe to do so is not a traffic infraction under Kansas law, the court held, and Trooper Lowell conceded in his testimony that the circumstances at the time did not make Mr. Lopez’s conduct unsafe {viz, there were no other cars nearby, the driving conditions weren’t hazardous, etc.).
Although the district court recognized that the stop nonetheless could be considered lawful as an investigative detention if Agent Suchma acquired reasonable suspicion Mr. Lopez was involved in criminal drug activity before he asked highway patrol officers to stop Mr. Lopez, the court ruled that the observations of the surveillance agents did not provide reasonable suspicion of such conduct, though the court considered this a “close call.”
After the district court issued its order suppressing the cooler’s contents, the government filed a timely notice of appeal. In its appeal, the government did not contest the district court’s ruling that there was insufficient evidence of a traffic infraction for crossing a lane marker to support a traffic stop, but argued that the circumstances surrounding the transfer of the cooler did give rise to reasonable suspicion of criminal activity sufficient to justify a brief investigative detention. At the same time, however, the government failed to certify to the district court, as required by 18 U.S.C. § 3731, 1 that its interlocutory appeal was not taken for purpose of delay and the suppressed evidence was a substantial proof of a fact material in the proceeding. In light of this deficiency, we entered an order to show cause why the case should not be dismissed. In response, the government filed the required certification and represented that its failure to file the document earlier was an oversight. During the briefing of this appeal, the government filed an unopposed motion (which we now grant) to supplement its response to our order to show cause, appending three sworn affidavits from the government attorneys involved in this case.
*795 In its filings, the government explained that a Section 3731 certification was not filed because the Assistant United States Attorney (“AUSA”) who prepared the notice of appeal was relatively new to federal practice, this was his first appeal of a suppression order, and he was unaware of the certification requirement. The government also detailed the analysis the involved attorneys undertook before deciding to appeal. In their affidavits, the three attorneys represented that, over an extended number of days, they each considered the merits of an appeal, discussed with each other and other attorneys whether the case should be appealed, and prepared an internal memorandum analyzing the merits and demerits of a potential appeal. They each also represented that, at the time they filed the notice of appeal (or requested that the notice be filed), it was clear to them that a Section 3731 certification could have been filed in good faith. Finally, the government represented that it has “assured that all [AUSAs] in the District [of Kansas] have been directed to familiarize themselves with” the necessity of complying with Section 3731’s certification requirement, Appellant’s Br. at 17, and that the prosecution of Mr. Lopez will be “substantially impaired, and probably defeated” if the drug evidence remains suppressed, id. at 20.
II
Failure to file a Section 3731 certificate within 30 days after an adverse district court decision does not deprive this court of jurisdiction but instead poses us with a discretionary question.
United States v. Welsch,
In deciding whether to exercise our discretion to hear an appeal, we are guided by Congress’s express purpose in enacting the certification requirement — namely, to ensure that government attorneys make “ ‘a thorough and conscientious analysis of the case
before
deciding to appeal.’ ”
United States v. Carrillo-Bernal,
For example, in
Carrillo-Bernal,
we dismissed the government’s belatedly-certified appeal because the government admitted that it appealed “in haste” almost immediately after learning of the district court’s ruling and made no demonstration that its decision to appeal was preceded by “a reasoned determination as to the considerations that Congress has expressly incorporated into Section 3731.”
Carrillo-Bernal,
To be sure, the government in
Carrillo-Bernal
argued that, even if it had failed to conduct a pre-appeal analysis of the case, the matter was of sufficient importance that equity demanded its consideration, and we have recognized such an exception to the prior-consideration rule.
Id.
at 1496-97;
see Hanks,
In
Hanks
the government did not address the certification issue at all in briefing, despite a jurisdictional motion and briefing by the defendant; instead, this court had to inquire about it at oral argument and order supplemental briefing post-argument.
Hanks,
In contrast with these cases is
United States v. Shareef,
We believe this case falls on the Shareef, rather than Hanks/Carrillo-Bernal, side of the line. Apparently, the only reason the government failed to file a timely certification was due to the relative inexperience of the AUSA who filed the notice of appeal — and the government stresses it has addressed the matter with the AUSA in question and taken steps calculated to minimize the recurrence of this problem in the future. The uncontested affidavits before us reveal that the government did, in fact, undertake a reasoned pre-appeal analysis of the Section 3731 factors, involving a number of attorneys thinking about this case over an extended number of days who prepared a written memorandum analyzing the proposed appeal. The affidavits before us each also represents that, at the time the government filed the notice of appeal, it was clear to the involved attorneys that a Section 3731 certification could have been filed in good faith' — that is to say, that the appeal was not for purposes of delay and the evidence was a substantial proof of a fact material in the proceeding. Given the uniformity of the evidence that the government complied with the substance if not form of Section 3731, we are obliged to entertain this appeal and have no need to reach the government’s alternative argument that this case presents the sort of *797 important legal question in need of appellate resolution that Carrillo-Bernal indicated could merit an exception to the prior-consideration rule.
Mr. Lopez responds that, even if the government did comply in substance with Section 3731’s requirements, his right to a speedy trial and need for protection from the hazards of prolonged litigation should nonetheless dictate dismissal of this appeal. While the delayed resolution of a case surely can weigh heavily on a criminal defendant’s mind,
see Hanks,
Ill
Turning to the merits, we begin by noting that the facts surrounding the surveillance of Mr. Lopez are not meaningfully in dispute. Accordingly, the only question before us is their legal significance, a question we review
de novo.
In assessing the constitutionality of an investigatory stop, we ask whether the circumstances demonstrate that law enforcement officers had reasonable suspicion that criminal activity may have been afoot.
United States v. Arvizu,
With these rules of review in mind, we consider the factors that contributed to the officers’ suspicion in this case. The officers saw a rendezvous in *798 which Mr. Lopez’s truck, after idling for an hour, moved in concert with the green truck from the hotel to the drive-in restaurant. They saw the passenger of the green truck, Mr. Urena-Bonilla, deposit the cooler into the bed of Mr. Lopez’s truck. They then saw Mr. Lopez promptly leave the restaurant for the interstate. Agent Suchma and Lieutenant Catania each testified that, based on his training and experience in hotel drug-interdiction surveillance, an exchange of this sort was indicative of illegal activity. Agent Such-ma testified that “it is not uncommon to find coolers, ... things of that nature, exchanged in a public area; and it is not uncommon to later find that those ... containers or coolers contain either drugs or a sum of bulk currency.” Hr’g Tr. at 21. Lieutenant Catania testified that “one of the things that we would watch for ... was an exchange of some sort, somebody bringing a vehicle to somebody ... or an exchange in the parking lot or meeting with somebody else at an alternate location and.then an exchange being made. Those are the things we typically saw, and the fact that one was made in this case made it very suspicious.” Id. at 100.
The officers observed this hand-off in the context of other suspicious circumstances as well. First, they saw what appeared to be counter-surveillance by the driver of the green truck, Mr. Cardenas-Corona. Second, there was a dearth of communication between the parties to the exchange. Although all three parties to the transaction were standing outside their adjacent vehicles in the parking lot, the officers observed no customary greeting or words exchanged between them, no acknowledgment of each others’ existence. Only when Mr. Lopez backed his truck out of the parking space to leave the restaurant did he and the passenger of the green truck briefly appear to speak to each other. Third, the parties moved their trucks from the hotel parking lot to the adjacent drive-in restaurant parking lot, where the hand-off took place, even though neither appeared to order or receive any food at the drive-in or enter the restaurant.
The district court did not include any of these three circumstances in its reasonable suspicion analysis, perhaps because they represent omissions, or things that didn’t happen. But the government reminds us of the logical significance of the dog that didn’t bark, 2 and we believe that omission of an expected or customary action, equal to actions themselves, can be of use in assessing whether something is amiss and criminal activity may be afoot.
Mr. Lopez responds that Agent Such-ma’s testimony does not indicate that he or his team inferred that Mr. Cardenas-Corona was engaged in counter-surveillance, so we should not consider that factor as contributing to reasonable suspicion. But Agent Suchma testified that an agent on his surveillance team saw the driver of the green truck exit his truck at the drive-in restaurant and stand around, looking about while the passenger put the cooler in the bed of Mr. Lopez’s truck. Hr’g Tr. at 18, 38-39. He then testified that, based on this observation, he thought, “in the event this guy is trying to conduct some type of countersurveillance, I was not comfortable with where I was,” so he moved his vehi *799 cle, because he “didn’t want to compromise the surveillance.” Id. at 39. Agent Sueh-ma’s testimony is easily understood as saying that he took action to preserve his cover based on his inference that the driver was engaged in counter-surveillance. Mr. Lopez does not contest that a reasonable officer could make this inference, and Agent Suchma’s testimony indicated that he did so, which contributed to his reasonable suspicion.
To be sure, as the district court correctly noted, some of the other factors identified as contributing to the officers’ suspicion are relatively weak. For example, the government’s reliance on the fact that Mr. Lopez traveled from a known drug source area is a factor that we have previously held so consistent with innocent activity as to “do[ ] little” when standing alone to add to the reasonable suspicion calculus.
Guerrero,
But neither of these factors stands alone in this case or is even necessarily essential to our conclusion. Rather, the exchange of the cooler and the circumstances surrounding the exchange, considered as a whole and with the due deference commanded by our precedent to the officers’ experience and training, suggest that reasonable suspicion of criminal activity existed sufficient to justify a brief investigative detention. In reaching this conclusion we are mindful that the level of suspicion required for reasonable suspicion is “considerably less” than proof by a preponderance of the evidence or that required for probable cause.
United States v. Sokolow,
In fact, this court has found even probable cause to arrest, above and beyond reasonable suspicion, based on a defendant’s suspected counter-surveillance incident to a drug deal. In
United States v. Soto,
* * *
The district court’s suppression order is
Reversed.
Notes
. The pertinent portions of 18 U.S.C. § 3731 state:
An appeal by the United States shall lie to a court of appeals from a decision or order of a district court suppressing or excluding evidence ... not made after the defendant has been put in jeopardy and before the verdict or finding on an indictment or information, if the United States attorney certifies to the district court that the appeal is not taken for purpose of delay and that the evidence is a substantial proof of a fact material in the proceeding.
The appeal in all such cases shall be taken within thirty days after the decision, judgment or order has been rendered and shall be diligently prosecuted.
The provisions of this section shall be liberally construed to effectuate its purposes.
. In Sir Arthur Conan Doyle's story, Inspector Gregory posited that a stranger had stolen a race horse from Colonel Ross's barn in the night. But Sherlock Holmes asked how he could explain the "curious incident” of the guard dog's silence. Holmes later revealed that the dog was silent because the thief was the horse’s trainer, a person familiar to the dog. See Sir Arthur Conan Doyle, Silver Blaze, in The Memoirs of Sherlock Holmes (1894).