Peterson, along with Heldorf, was a scientist hired by Carrington to examine his captive aliens. He was shot and killed by one of Reegan's thugs when he tried to attack him. (TV: The Ambassadors of Death)
Behind the scenes
Peterson is never identified in the episode, only in the paperwork for episode three. The actor who portrayed Peterson, Roy Scammell, was a stunt performer on the series and played Peterson without credit.