There are a number of Columbo episodes I've noticed that have a situation where the killer commits an initial murder that could have been explained in a way that might have gotten them off the hook (accident, self-defense) or at the very least generated some sympathy for them, but then they go on to commit a second murder that is clearly premeditated and makes it impossible to have any sympathy for them or any sense that they could get off the hook.

#1-"Lovely But Lethal". Viveca's killing of Carl Lessing is clearly an accident, and he may have been on the verge of getting violent with her which prompted her to hit him with the microscope. But then the murder of the secretary is pre-meditated.

#2-"Dagger Of The Mind." Sir Roger's death is clearly an accident. Then we have the premeditated murder of the blackmailing butler.

#3-"A Deadly State Of Mind." Another case of an accidental death, that could even have been partial self-defense that gets compounded by Dr. Collier's premediated killing of Nadia Donner.

And if anyone had a tiny drop of sympathy for Paul Galesko being driven to kill his wife in "Negative Reaction", framing and killing someone else for it would certainly dispel that!