I think they both shaved all of their upper body hair. Maybe it made strapping bombs to their chest easier and they planned on doing that at some point? I don't know. Younger bro was also hairless when they got him.
Hate to say it (since I don't buy any of the conspiracy nonsense), but body shaving does seem to be characteristic of Islamic terrorists. The guys who hijacked the planes on 9/11 all shaved their bodies.