A competent United States Attorney should easily win any federal drug case. The elements of federal drug crimes are easy to prove, easy to explain, and easy for juries to comprehend. Why then does the government need members of law enforcement to testify as experts in federal drug prosecutions? The answer: they do not. Yet district courts routinely admit (and appellate courts uphold) expert agent and officer testimony on a wide array of drug topics—including when officers testify both as expert and lay witnesses. Were the examples of law enforcement expert testimony few, perhaps no problem would arise. But this problem is pervasive.By frequently allowing members of law enforcement to testify in easily proven drug cases, federal district courts neglect their “gatekeeper” role to admit only reliable expert testimony. More problematically, officers’ expert testimony may implicitly comment on defendant’s mens rea, thereby reducing the prosecution’s burden to prove all elements of a criminal offense beyond a reasonable doubt. Yet, the fix is startlingly easy: the federal judiciary should disallow members of law enforcement from testifying as both an expert and lay witness in federal drug prosecutions. And, before admitting officer expert testimony, district courts must vigilantly guard against proposed officer testimony that is either empirically invalid, or could inappropriately comment on defendant’s mens rea.Doing so would allow federal courts to meaningfully resume their roles as gatekeepers while simultaneously enabling the jury to perform its duty as fact-finder.
Gallini, Brian, "To Serve and Protect? Officers as Expert Witnesses in Federal Drug Prosecutions" (2011). School of Law Faculty Publications and Presentations. 36.