I just watched this for the first time as well and I noticed a lot of plot holes like these. I'd heard it was a weak Columbo but I actually enjoyed it a lot - both Peter Falk and the guy playing the murderer are on form and there are a lot of classic elements. However, the story is weak on many different levels. As well as the points noted above, running someone over in their drive is a messy and unreliable way to kill someone (surely the coroner would have spotted how he was killed right away), plus the victim had loads of time to get out of the way. The biggest plot hole of all revolved around the victim's wife, who seems not the least bit upset about her husband's death and implausibly refuses to break patient confidentiality when Columbo shows her the missing file, which clearly implicates the son or his father. At the beginning of the story, the victim tells his murderer that he and his wife both know about the plagiarism so why aren't both murdered and why is the wife so reluctant to face up to the obvious connection between this and her husband's death? There are hints that she and the son are having an affair but Columbo's bluff at the end is done in such a way that it is never clear whether they are or not. If she was, her story would make more sense.