Continuity mistake: During the scene where Ness kills the Italian mobster in the lodge near the border, the moment he shoots him the wooden rail behind has two sticks underneath, half a second later, when the mobster is flying backwards dead, the sticks disappear, and a second afterwards, when he is laying dead, the rail's appearance has nothing to do with the previous two.
Visible crew/equipment: When the man who's sent to kill Malone goes to his house, a shot seen from his perspective shows the house's windows, on which the cameraman is reflected while passing in front of them with the steadicam. (01:19:21)
Answer: Ness was coming to Malone's apartment to discuss the information with him there, Nitti and his men just got there first.
Captain Defenestrator