Odds are he was very stupid. They use a HK .40 and it's required to be holstered unless needed. Holstered guns with the safety on don't go off. He had to be handling it, while on approach, for no good reason.
Personally, I was suprised they picked HK. Heavy gun and I'd think a Glock, S&W M&P or a Springfield XD would be safer...especially the XD with the grip safety along with the trigger safeties.