The hitman at the end of Casino is played by Frank Cullotta, a real-life mobster whose career in the Chicago/Las Vegas mob gave inspiration to the film.
Frank Culotta, though not a Las Vegan, was a technical consultant on the film, since he knew Tony Spilotro since they were children and was the Ant’s right-hand man in Vegas.
In the scene where the hitman is chasing the target through his Las Vegas house, the actor playing the shooter just couldn’t get it right. Scorcese said to Frank, “Show him how you did it.” (Yes, Cullotta himself had assassinated Jerry Lisner, who’d provided information to the police about crimes that Cullotta and Spilotro had committed.)
Frank acted it out so realistically that Scorcese put him in the movie to film that scene.