Blooper

When Abigail and Edmund are signing their wills, the lawyer Martin takes Edmund's from his hand and closes it. As the camera turns to a new angle, it shows both wills open on the desk, and only then does Edmund close his will and hand it to Martin.

When Columbo gets up from the antique chair, he takes his cup and saucer with him to the door. He never sets it down, but once he's outside, he no longer has them.

(at around 51 mins) During Columbo and Abigail Mitchell's meeting at the dock, Columbo bends down to unhook Dog's leash while Dog is facing the ocean. When the shot changes, Dog is facing the opposite direction.

When Abigail and Edmund are signing their wills, Abigail holds Edmund's will open with her left hand, while Edmund's will overlaps Abigail's. When the scene changes to an overhead shot, Abigail is no longer holding open Edmund's will, and neither will overlaps the other.

When Columbo is stacking the safe deposit boxes in the safe, there are four boxes for him to stack. He stacks the first two, then, when the camera cuts to a close up of his hands for the next box, he's stacking the fourth box, not the third.

Abigail locked her nephew in the safe, but it is a very big safe. It seems to be a room containing at least 20 cubic meters of air. If the nephew breathes normally, one cubic meter is more than enough for about an hour's stay, so he shouldn't run out of oxygen from one evening to the next morning. He ought to be alive and well when the secretary unlocks the safe.

(at around 17 mins) The plane seen in flight has no airline name on it. The only markings are Boeing and 747.

When Abigail locked her nephew in the safe, she looked at the alarm switch, which was turned off, hesitated, then closed the door. Later, Columbo tells Abigail that the alarm was turned on.

However, this was part of her plan, as she told Columbo later that she had forgotten to turn the alarm back on and had called her maid to turn the alarm on, thereby creating the scenario that he had accidentally locked himself in when the maid came in to reset the alarm.

(at around 12 mins) Edmund is driving away in his Mercedes 450SL. The sound heard is that of a 4 cylinder engine, but the 450SL is a V8.

A recording at normal volume cannot compare to a desperate man's shouting and banging on the door of a seemingly soundproof safe.

Abigail, supposedly a mastermind, chooses a very unreliable means to murder her nephew as Veronica could have opened the safe early enough to free Edmund and he would have had all the time to leave incriminating messages.

Not much of a preparation as Abigail tests her theory of the soundproof safe just hours before committing the crime, and after having asked her lawyer to draw the wills.

As soon as Martin tightens the screw holding the light switch to the wall bracket, he flips the toggle up, and the room lights come on. This indicates that he worked on the electrical connections to the switch without first cutting off power to the circuit by shutting off the circuit breaker in the breaker box, or pulling the fuse in the fuse box, elsewhere in the house. Working on a light switch without first shutting off power to the circuit in the room could have resulted in his electrocution.