We have an article collecting a handful of these in the Scrapbook (a bit fancifully and inaccurately called Cast Reunions), if you'd like to check that out, but it would probably be hard to beat Escape From Planet of the Apes, at least if non-killer Columbo actors are included: Roddy McDowall, Kim Hunter, Bradford Dillman, Wiliam Windom, Sal Mineo, John Randolph, Ricardo Montalban, even a cameo (according to IMDb) from Army Archerd. The original Planet of the Apes also of course had Maurice Evans.and if we're including others in the movie series, Conquest of the Planet of the Apes had France Nuyen, and Beneath the Planet of the Apes had James Gregory and Gregory Sierra. So, the Columbo and Apes universes clearly had a lot of overlap!
Thank you Dave, Ted and Grant! I was inspired to do a little research and found that there are a bunch of movies that starred multiple actors who played the killer on episodes of Columbo. The list is up to about 80 so far...I expect it to reach around 150. I've posted the list in progress on Letterboxd (link below). For those who just want to a good trivia answer...Name 2 films that each star 4 different actors who played killers on Columbo - 1976's Voyage of The ****ed (Faye Dunaway, Oskar Werner, Jose Ferrer and Lee Grant) and 1965's The Greatest Story Ever Told (Martin Landau, Donald Pleasence, Roddy McDowell and Jose Ferrer). There are 7 (so far) that starred 3 killers.
Link to the Letterboxd list...
https://letterboxd.com/daveyarddave/list/movies-that-star-multiple-actors-who-played/detail/
It's an early ' 70's TV movie, and most of those are very underrated.
You can find a whole lot of COLUMBO actors in general among early ' 70's TV movies, not necessarily ones who played killers, but actors in general.
Would a TV mini-series count on this list? One I'm very familiar with is "Captains and the Kings" from 1976, and (being such a long story) it has plenty of COLUMBO actors.
Robert Vaughn
Celeste Holm
Harvey Jason
George Gaynes
Bernard Behrens
Sean McClory
Sian-Barbara Allen
Ken Swafford
Robert Donner