Defendant-appellant Marco A. Echeverri asks us to overturn his conviction on two drug-trafficking charges. He alleges that the proof was insufficient to support the jury’s verdict; that the government never properly authenticated a “drug ledger;” and that the court below erred in permitting an еxpert witness to testify concerning the import of the disputed document. Discerning no error, we affirm.
I. BACKGROUND
We limn the facts in the light most favorable to the government, consistent with record support.
See, e.g., United States v. Maraj,
*677 Armed with a search warrant, a team of law enforcement officers including FBI Special Agent Frederick Ghio entered appellant’s apartment in Pawtucket, Rhode Island. The living quarters consisted of a narrow bedroom, a multi-purpose room, and a bathroom, having a total combined area roughly equal to that of a one-car garage. When the agents arrived, Victor Gallegо was leaving the bathroom and appellant was seated at a table in the multipurpose room. Next to appellant, on the couch and in plain view, lay an earnings statement in his name. On the back of this statement was a handwritten column of numbers arrayed in the following fashion:
1000
2000
17000
1000
10000
4000
1000
1000
34000
In the cоurse of the ensuing search the agents found a tape-wrapped block of cocaine — eighty-six percent pure and weighing about two pounds — on the toilet lid. The tape had broken and the contraband was exposed. An electronic scale lay nearby-
Gallego and Eсheverri were charged with possession of cocaine with intent to distribute it, 21 U.S.C. §§ 841(a)(1); 841(b)(1)(B), and with participating in a drug distribution conspiracy. 21 U.S.C. § 846. Gallego pled guilty and Echeverri stood trial alone. Over his objection, the government introduced the earnings statement into evidence. The court allowed agent Ghio to testify that, in his opinion, the reverse side of the statement comprised a drug ledger (the individual figures corresponding to per-ounce prices for various cocaine sales in the Rhode Island market). Ghio further testified that it was common for cocaine dealers to keеp their accounts in such fashion; that the going price for cocaine was $35,000 to $40,000 per kilogram; that the total shown on the earnings statement, if interpreted to mean “dollars” and added correctly, 1 corresponded in rough proportion to the gross sales price of the aggrеgate cocaine on hand; and that the quantity of narcotics seized was inconsistent with personal use.
The jury convicted Echeverri on both counts. This appeal ensued.
II. SUFFICIENCY OF THE EVIDENCE
Appellant labors to convince us that the judgment below rests on too fragile an evidentiary foundation. We аre not persuaded.
A. Standard of Review.
The standard of review applicable to sufficiency-of-the-evidence challenges is settled. An appellate court must examine the evidence in the light most flattering to the prosecution, indulging all reasonable inferences in its favor and then determining whether a rational jury could find guilt beyond a reasonable doubt.
See, e.g., Maraj,
B. Possession with Intent to Distribute.
In challenging his conviction on the specific-offense count, appellant questions whether the evidence is copious еnough to sustain a finding that he knowingly pos *678 sessed cocaine. The government, he says, proved no more than his “mere presence” at a site where drugs were found.
The “mere presence” defense has become, at one and the same time, both the last haven of the innocent аnd the last refuge of the scoundrel. Although courts have found it applicable in certain situations,
United States v. Barnes,
This is such a situation. There is far more to the prosecution’s case against Echeverri than his corporeal presence in the apartment. A rational jury, drawing reasonable inferences from proven facts, could certainly have concluded that this was a case of culpable presence as opposed to mere presence,
see Ortiz,
Both constructive possession and guilty knowledge may be inferred from a defendant’s dominion and control over an area where narcotics are found.
See, e.g., Barnes,
Moreоver, the entire apartment consisted of a small, cramped space. The cocaine was in plain view, resting openly on the dwelling’s only toilet. Tools of the drug trade were conspicuously displayed. Echeverri himself was physically present, seated within four feet of the contraband. All in all, the totality of the circumstances suffices to support both a finding of constructive possession and a finding of guilty knowledge.
See, e.g., United States v. Gonzalez-Torres,
The evidence was also ample to sustain a finding of scienter. We have repeatedly held, and today reaffirm, that an intent to distribute drugs can legitimately be inferred from factors such as quantity and purity.
See, e.g., United States v. Ocampo-Guarin,
We will not paint the lily. Because we require only that a jury’s verdict be supportable, not that it be inevitable,
see Boylan,
*679 C. Conspiracy.
Appellant’s challenge to his conspiracy conviction fares no better. To support a conspiracy conviction, the prosecution must prove certain things not required under the specific-offense count. It must show,
inter alia,
that an agreement or working relationship existed, thаt it had an unlawful purpose, and that the defendant was a voluntary participant in it.
See United States v. David,
In this case, there was evidence that, in a tiny apartment, within feet of the sole tenant, law officers found a commercially exploitable quantity of high-purity cocaine, a measuring scale of the sort frequently used by narcotics dealers to ply their trade, and a drug ledger (written on the back of the tenant’s pay stub). Exiting from the room where the cocaine lay open and exposed was another man (Victor Gallego). A jury viewing this evidence could reasonably conclude that the two men had agreed to disobey the law and distribute cocaine.
Cf., e.g., Ortiz,
III. OTHER ASSIGNMENTS OF ERROR
We consider appellant’s assignments of mid-trial error in the ensemble.
A. Authentication.
Appellant complains that the government failed to authenticate the so-called drug ledger as required by Fed.R.Evid. 901, and that, consequently, the district court erred in admitting it into evidence.
3
We review the trial court’s rulings сoncerning authentication of documents only for mistake of law or abuse of discretion.
See Ortiz,
When the authenticity of a document is challenged, the court must determine whether there is sufficient threshold proof that the document is what its proponent claims it to be.
See Ortiz,
In this instance, the government claimed that the earnings statement doubled as a drug ledger. The district court admitted the evidence on that basis. We discern no error. The earnings statement was clearly identified with Echeverri—it was, after all, a recapitulation of his wages, reposing in his аpartment. Federal *680 agents discovered the document lying on a couch within feet of a sizable, easily visible package of cocaine. The column of handwritten figures on the paper totalled 37,-000 — the approximate dollar value of the discovered cocaine in the local market. Finally, an agent familiar with the drug trade testified on voir dire that he believed the document was a drug ledger and gave persuasive reasons in support of that conclusion. No more was exigible.
To be sure, the government presented no direct proof that Echevеrri authored the jottings on the earnings statement. But, such proof was not a prerequisite to admissibility in the circumstances at bar. On the record before us, the government sufficiently connected the document to the conspiracy and to the appellant, even though it did not conclusively рrove the author’s identity.
Cf, e.g., United States v. Natale,
B. Expert Testimony.
Appellant also contends that the district court erred in allowing agent Ghio to offer opinion evidence anent thе drug ledger. His contention is unavailing.
We have consistently recognized that academic training is not a sine qua non of expert knowledge concerning the practices of hard-core drug traffickers.
See, e.g., United States v. Hoffman,
In deciding whether to admit or exclude opinion evidence, courts must.assess whether the testimony will likely assist the jury in understanding the proof or ascertaining the facts.
See
Fed.R.Evid. 702. Because of its first-hand aсquaintance with the case, the trial court enjoys broad leeway in making this discretionary determination. The court of appeals will overturn a trial-level determination about the need for expert testimony only if a manifest abuse of the trial court’s discretion is in prospect.
See Ladd,
Herе, the central issue on count 2 was whether appellant was — or was not — a knowing and intentional participant in a cocaine conspiracy. Ghio’s testimony was clearly relevant to that issue. Moreover, the testimony was undoubtedly helpful to the jury. Laymen, on average, are not familiar with the praxis of the cocaine community.
See Ladd,
IV. CONCLUSION
We need go no further. The government proved Echeverri’s guilt beyond a reasonable doubt in a trial free from reversible error. The judgment below is therefore
Affirmed.
Notes
. The column of figures, added correctly, totalled 37,000, not 34,000. We consider this mathematical mishap unimportant.
. The fact that appellant, as the sole rent payer and resident of the dwelling, had the exclusive right to control thе comings and goings there is one of several important distinctions between this case and
United States v. Ocampo,
. The rule provides in pertinent part:
The requirement of authentication or identification as a condition precedent to admissibility is satisfied by evidence sufficient to support a finding that the matter in question is what its proponent claims.
Fed.R.Evid. 901(a).
. The cases cited by appellant in support of his challenge are readily distinguishable. In both
United States v. Mouzin,
. We note that the district court wisely instructed the jurors that agent Ghio’s opinion testimony, like opinion testimony generally, was not binding upon them.
