When Elizabeth is shot in the video playback, the killer supposedly shoots her from off-screen to the right side of the screen. However, the puff of smoke comes from the left side of the screen.
Martha Scott is clearly breathing as the killer steps over her corpse and leaves the manor.
Trivia: For the first time, Columbo fires a gun. However he doesn't aim at someone, it's just to prove a theory about the doors.
After the "accident," Cadet Morgan tells Rumford that all the cadets are in the chapel, as ordered. A few minutes later, we see a group of cadets walking beside a building.
Columbo must wait for what seems like an eternity while the computer prints out the information he requested on Lewis Lacey. Finally, the computer stops. The last line printed on the form is "MORE?".
Columbo's last line said that Janus's confession was going to hang him. At that time, California used the gas chamber.
When Milo Janus starts the movie for his party guests, the take-up reel holds about two-thirds of the movie, while the supply reel (front) only one-third. In other words, the movie is already about two-thirds finished.
Furthermore, he had earlier mentioned to Buddy that this was going to be an "uncut X rated" film. The one being shown does not even remotely resemble that kind of film. The group he has over does not appear to be the type to watch that type of film either.
In the opening sequence, Milo's secretary (Gretchen Corbett) is supposed to be recording an incoming telephone call, but doesn't depress the record button (small red button) on the tape recorder. Technically, the tape recorder is in playback mode.
When Columbo is speaking with Milo Janus in his office after he's been doing exercise his track suit is all sweaty, but when they meet in the corridor a moment later it is clean.