HAN SHOT FIRST. Got it?
Han always shoots first. Name me one scene that had shooting and an armed Han in it where he didn't shoot first? The very first time we see him run into Storm troopers in docking bay 94, he shot first. On the Death Star he charged into a whole room filled with a battalion of Storm Troopers, he shot first. Shooting his way back to the Millennium Falcon, he shot first. He totally punks three tie fighters when Luke is lining up to blow away the Death Star, he shot first. Gets cornered on Hoth in a malfunctioning Millennium Falcon, he shot first. He sees Vader for the first time on Bespin, he shot first. He totally blundered his way around Endor trying to sneak up on those Forest Troopers but at least he got off the first shot.
Han shoots first, end of debate.