I happened to watch Columbo cries wolf with my wife the other night and she brought up an interesting point. The second time that Columbo goes into the Chateau, he immediately goes upstairs and starts looking through Diane bathroom, jewelry, Etc. Would this constitute an illegal search? At the point that he is in their house, he has not yet running to Sean Brantley to serve him with a search warrant yet there is looking through everything. I wonder if that would have gotten thrown out in court. Since that search was illegal, or so we think, I wonder if the whole case gets thrown out. Interesting contemplation.

If you pay close attention throughout the entire series, Columbo doing things he shouldn't be doing to catch someone happens quite a bit. Like Columbo carrying a piece of evidence around with him until he catches the killer. Chain of evidence is lost and that piece of evidence gets thrown out in court. As far as his illegal searches go, as Columbo says Double Exposure, he's not searching, he's looking.

Somehow the SMALLEST case of that that I can think of is the one that bothers me more, and that's the locker in RANSOM FOR A DEAD MAN. Partly because of how EARLY it is - as if even Columbo shouldn't suspicious of the right person THAT early.
Also, Leslie is the kind of person you'd expect to keep it locked (sort of like Gene Stafford).

At the other extreme, there's the semi-comical one with Danny Goldman in DOUBLE EXPOSURE -
"We're not searching, we're looking."

In "Dead Weight" when Columbo arrives at the General's house, he tells the officer to check the yacht and that side of the house. The officer states he needs a warrant, Columbo tells him that he will ask the General permission. Did he ask the General's permission?

I'm sure if we over analyze every episode we could find at least one example of something Shady that the lieutenant did. As he stated in Columbo Goes to College, "there's very little that he wouldn't do to solve the case."

Here is a for instance. In Ransom For a Dead mMan, he looks through Mrs. Williams' locker, more specifically at the bag that she had in there. After the money drop.