Just noticed something funny, in the scene right after Columbo shows up at the murder scene, he gets a call, he asks the Janitor where he can take the call, 'in the office right through that door'... Columbo is walking towards a door, the camera swings around as he's walking and you can now see in the room he's walking into... look carefully at the silhouette of a chair in the background, you'll see a head that pops-down behind the chair!

great spot I'm off to check it out