Carolyn Grant is wearing a coat when she gets off the boat, but she didn't have one when she got on.
She had her coat in her left arm along with her purse when boarding the boat.So this proves that she was able to wear coat when stepping off the boat later that evening.
When Harlow Grant and his girlfriend are driving in her car after he's been released by the police, the rear view mirror is missing from the windshield in the two-shot, but it's there in the long shots.
All of the art in the gallery is packed up to be moved into storage yet the final scene reveals there are two paintings still in the windows that were missed.
At the scene of the crime, the police are not at all interested in checking for fingerprints. They put their bare hands on everything from doorknobs to the telephone to art objects to the stair railing with no regard to checking for prints that might help to identify the culprit.