Abelino Mazaniego, 47, was rushed to Overlook Hospital on July 17 after being beaten while sitting on a bench in Summit.
Three teenagers are charged in the attack, which was videotaped.
Police say Stephan Randolph, a nurse at Overlook, stole hundreds of dollars from Mazaniego while he was unconscious in the emergency room.
"This is a sad and horrible addition to an already unthinkably tragic incident," said Joan Lebow, Director of Communications for Atlantic Health, which runs Overlook. "Our hearts go out to the victim's family that has already suffered so much."
Randolph, 39, of Flemington has been fired, Lebow said.