Kannibal (2001)

A squad of police cars responding to an emergency call races through the streets of Atlanta. Upon arrival at the crime scene, they see complete desolation. Dead bodies are everywhere. And they apparently just missed the killer, though one of his victims, the head of New York's Russian mafia, survived. The family's crime operation then comes to London, but unknown to them, the assassin has also moved there and is working for the police as a pathologist. And while the family is still hunting the assassin, he is on his own mission of revenge.