I have been searching for this answer for years. The person isn't listed in any credits, and somebody once gave me the name of Jeff Anders Ware. I contacted Jeff and he said he didn't play DB but played in the Mona Lisa episode.

Long story short, just always wanted to know who this "actor" was. Truth be told, he could even be dead at this point as that episode is from October 1988 and he appeared to be late 50s or early 60s even at that point.

If anybody can help, that would be great.

I remember watching this segment on youtube and someone in the comments said they knew the actor. They gave his name. No way to see it now.

I think I've finally solved the mystery! Here's an obituary for a gentleman named Gary Mortenson, who passed away in 2006. It states that he played D.B. Cooper on "Unsolved Mysteries":
http://magicvalley.com/lifestyles/announcements/obituaries/gary-mortenson/article_9dd4f1d8-ad5e-59a1-b81a-459fa6a9ff8e.html

I did a bit more digging and apparently, he was not a professional actor, but the got the gig because he was friends with a producer on UM.

Yeah, looks like that's him. The person on youtube said they knew him personally.

I saw an Episode of Quincy yesterday which was obviously based on this case, the guy was the only man in history to hijack a plane with a biological weapon, he parachuted out with the money, but got hung up in a tree, was murdered & eventually the town was an Anthrax zone.

It sad I finally find this out now, but thank you so much. Seems he died 10 years ago, and was only about 50 when he played 'cooper' in the episode.

I had been trying to find out who he was since the early 2000's, perhaps had I know this then I could have contacted him somehow back then.

Thank you all!!