There's also Negative Reaction - which is interesting for another reason:

Not only do we never see Bart Kepple's home, we also never see his wife.

In fact, until Bart mentions her to Columbo on the golf course, you don't really get the feeling he is married. It's his explanation for not saying he knew Tanya Baker.

So, that opens another thread. Are there other Columbo's where the murderer's husband/wife is mentioned but we never see them. (Aside for Ransom for a Dead Man where the husband is the victim).

Oops, I got the wrong title. Of course it's "Double Exposure" as in the list, but still the bit about his wife stands.

That's a great observation, RoyalFool! And it would be interesting to know whether there are other examples. Now, I can't exactly remember if Joe Devlin in "Conspirators" was ever implied to have a wife back in Ireland, but it seems like it could have been hinted at. (On the other hand I could be completely wrong; it's been awhile since I saw that episode, even though I like it quite a bit.)