I don't see how tommy brown would've murdered columbo in a car, he didn't have a gun and columbo murderers tend to only know how to murder in the same way (see paul gerard retrying to poison columbo after using the same method for vittorio rossi), but makes sense for the other 2 examples; also if eliott blake decided to not murder columbo with the guillotine, maybe to see where columbo's investigations were going, ironically columbo would've died there due to having the labels switched.