Upon reviewing "Double Shock's" ending again, I realized that it's really not very similar to "Dead Weight's" ending at all; somehow I had thought there was a conversation between Columbo and Mrs. Peck in a similar vein as his talk with Helen Stewart.
In regards to "Dead Weight", one aspect of the ending that really stands out to me is Hollister very sincerely telling Helen that he's sorry. One expects the murderer to be apologetic towards someone directly hurt by the crime that was committed ("Etude", "Death Lends A Hand"), but not toward a dispassionate witness to the crime, although, obviously, Helen became more than that.
Indeed, Hollister shows greater remorse toward having hurt Helen than Harold Van Wyck does toward his devoted wife of (presumably) several or more years in "Playback" (an episode with, I feel, an outstanding ending, as well).

re..dead weight...one of my LEAST fave episodes
an interesting story from Suzanne Pleshette

http://www.youtube.com/watch?v=k9qjn18ohR0

"The conspirators".

We discover where they hide the pistols at the end and the solution is nothing less than surprising !