The bodyguard has a Taurus PT92,
which the detectives suspect is the murder weapon from a night club. Turns out there's a Glock 9mm involved, which is the actual murder weapon. Taurus' have a traditional "land and groove" rifling to the barrel. (Imparts spin to the bullet.) Glocks have a spiral hex shaped bore which compresses the bullet. Had the victim been shot with a Glock, the cops would have known immediately the bodyguard's Smith couldn't be the murder weapon.