Whether law enforcement expert testimony contradicting percipient witnesses satisfies Federal Rule of Evidence 702

QUESTION PRESENTED Law enforcement expert witnesses have become an increasingly indispensable staple for the government in criminal trials. The first witness is a uniformed officer appearing as the government’s ‘overview’ witness, who tells jurors what the government’s case is expected to be. The last witness is another uniformed officer appearing as the government’s ‘summary’ witness, who neatly packages the government’s case in a way designed to make it unnecessary for jurors to deliberate at all. Interspersed between these first and last witnesses are often countless officers who inject key buzzwords into the trial that remind jurors of the inherent danger posed by persons similar to the defendant. The use of so many law enforcement ‘experts’ can make it possible for the government to present its case without the need for actual percipient witnesses at all. The issue in this case involves just such a situation. Where all the percipient witnesses in a case have testified in a manner unsatisfactory to the government’s prosecution, under Federal Rule of Evidence 702, which requires an expert’s testimony to “help the trier of fact to understand the evidence or to determine a fact in issue,” may the government be allowed to introduce law enforcement ‘experts’ to provide testimony that contradicts its own percipient witnesses in order to make its case? Should these officers have any limitations placed on their testimony?