In many cases throughout the series we see suspects offering "too much" help to try and take suspicion off them. For instance:

Justin Rowe and Cooper (Columbo Goes to College)

The Commissioner (a Friend in Deed)

Abagail Mitchell (Try and Catch Me)

The list goes on while Columbo continues to give them rope to hang themselves.

In the movie COMPULSION, the fictional version of Richard Loeb (played by Bradford Dillman) keeps trying to help the police since he knew the victim and knows the neighborhood. I don't know many true crime stories remotely well, but I've heard that Richard Loeb really did do that!