The chap wearing the armour is Nik Sant (AKA 'Gramps'), one of the Endor Strike Team who assaulted the base.
The armour belongs to the imbecile pictured below, listed as "Unidentified Scout Trooper" in the credits but almost certainly played by Peter Diamond who also portrayed a Stormtrooper, a Death Star Trooper, a Snowtrooper, a Scout Trooper and a Rebel Commando.
It may interest you to know that the film's novelisation states that the hapless stormtrooper was rendered unconscious rather than being killed:
Back at the bunker, the last scout was undone. Subdued by Chewbacca, bound, stripped of his suit, he was being carried into the woods now
by two other members of the strike team.
Leia peeked inside. No sign of life. She motioned the others, and
entered the bunker. Han and Chewie followed close on her heels. Soon
the entire team was huddled inside the otherwise empty steel corridor,
leaving one lookout outside, dressed in the unconscious scout’s
uniform. Han pushed a series of buttons on the inner panel, closing
the door behind them.