I have never understood why Kay just tossed the glove onto the floor of the projection booth; and I never understood why Walter didn't just pick it up and toss it out long before the Columbo showed up the following morning (I assume it was morning). Kay could have put the glove anywhere, yet she hap-hazzardly throws it on the projection room floor -- rookie mistakes.
I'm a total sucker any time somebody posts about Kay's mistakes in this episode. There really isn't ANY valid reason that she wouldn't have, at the very least, picked up the glove, if she had any clue about powder burns, etc.
And the other piece that hung her, she had plenty of time to STOP having her dry cleaning delivered to the place of the man she murdered, but NOPE...didn't do that either.