A few days ago I was watching Suitable for Framing and in the opening scene it suddenly occured to me that one major clue never gets mentioned.

In Ransom for a Dead Man, Columbo makes a big thing about the dead man having been shot by someone who was sat down at the time. In Suitable for Framing Dale kills his uncle while his uncle is sat at a piano playing a tune. It would be obvious to the coroner that the angle of the bullet was consistent with Rudy being sat down and the killer stood to his right. The doctor says Rudy was killed by a single bullet almost instantly so there's no way the body could have fallen half a mile from the piano stool and, there's the case of blood splatter and blood from the wound getting everywhere and making the moving of the body impossible to hide if Dale wanted to. That would mean that Rudy knew his killer and that it couldn't have been a gang of art thieves.

This would help Dale in his quest to frame his Aunt.

I wonder why they didn't inlcude this in the story?

In “Ransom for a Dead Man”, I think the issue that Columbo raises is that the murderer was sitting down, waiting to ambush the victim.