Visible crew/equipment: When SFC William James goes through the plastic sheeting to see a dead body on the table, you can see an ungloved, crew member's hand open the entrance for him. (01:20:40)
Continuity mistake: At the start, the guy is putting the bomb suit on and the collar is down. Camera cuts and the collar is up. (00:04:45)
Answer: The problem for the sniper was once he'd taken his shot, he was now pretty exposed. He didn't have a lot of cover and it wouldn't have taken the Americans long to figure out where the shot came from, hence why the enemy snipers made no attempt to move.
GalahadFairlight