I think Brimmer would have been on his guard when Columbo told him word for word what he thought happened while they were having lunch in Brimmer's office.

That’s true. “Our killer has a bad temper”, and “we’re looking for a left-handed man with a ring...as a matter of fact just like yours” weren’t subtle hints. He was challenging Brimmer. But why tell Brimmer that he wanted the killer to look for the lens. He DID actually want the killer to look for the lens. He knew Brimmer was the killer and Brimmer knew about the missing lens already. So why state it out loud to Kennicut?

I guess it was just to reinforce the plot line.

“Troubled Waters” is another example where the murderer was well aware of Columbo’s suspicions and should have seen through Columbo’s obvious statement about how finding the gloves with the powder burns would close the case.

These are all excellent examples. That's why I love this forum so much. Because things that I don't remember or don't think of you guys remind me of. It's great.