When we see Milo put the weight on Stafford's neck, we only see him place one of Stafford's hands on the bar bell. Funny also however that in an un-columbo like way, the lieutenant doesn't pick up on it. I can see him asking Milo Janus "How do you explain that only one side of the bar bell has fingerprints on it? I mean sir, nobody would be able to lift that bar bell with one hand, it would be way off balance as well as being too heavy."

Ironically, Columbo does pick up on the fact that the paper in Wade Anders' printer has no prints on it in "Caution - Murder Can Be Dangerous to Your Health."