This has come up here before. And frankly, I find it all very confusing!!
Someone in the past posted about an early scene where Columbo does see Wilson using the metal detector. I have never seen this scene.
But even if there wasn't a prior scene to when Columbo uses a metal decector in the final scene...it doesn't take any credibility away from it. Columbo obviously knows that Wilson is into gadgets...and it can easily be assumed that the 2 of them may have talked about how the different gadgets worked...even though it wasn't shown in the episode.
Ok....now I am confusing myself!!
I just looked at an old tape of this episode that the BBC broadcast years ago - still no sign of the elusive scene. I tend to think it's a trick of memory. We see Columbo looking a bit troubled when he realises his idea for making casts of footprints is out of date, and then we see the metal detectors being established in a separate scene.
Having Wilson actually explain metal detectors seems too "on the nose" for me. I don't think it would establish it for the ending, rather it would make it too obvious. Much more likely, knowing his personality, that Columbo would have gone to someone at the department and said, "I hear you have things like night cameras and 3D photos now. What else do you have that might be useful to me?"
I received your DVD of, "Candidate For Crime" today and I'm in the middle of watching it now. The picture and sound is TOP QUALITY! Excellent all the way. I haven't seen that original intro since it first hit NBC-T-V many years ago!
I want to thank you so very much for being such a GREAT guy and making me and I'm sure the rest of us Columbo fans very, very happy!!