I noticed when watching Troubled Waters that two of the actors had been other Columbos, Robert Vaugn and I forget his name but he was in Dagger of the Mind.
There's even three of them. In addition to Robert Vaughn and Bernard Fox, we also have Dean Stockwell. He played the murder victim in The Most Crucial Game, and in this episode he plays the band member whom Vaughn's character is trying to frame for the murder.