United States v. Lopez-Medina, 461 F.3d 724 (6th Cir. 2006).
Federal Evidence Review draws attention to this case on the issue of law enforcement testimony. The case involved drugs. In military prosecutions we have similar situations where law enforcement testifies about drugs.
The circuit concluded that plain error resulted: “We conclude that permitting police officers to testify as experts in their own investigations and give opinion testimony on the significance of evidence they have collected, absent any cautionary instruction, threatens the fairness, integrity, and public reputation of judicial proceedings, regardless of whether the defendant is actually innocent.” Lopez-Medina, 461 F.3d at __.