The sad thing is that he's probably very good with firearms,,,he just a made very bad mistake.
About 10 years ago we had served several warrants for narcotics,,,after doing this we "SWAT" went back to the range to complete some moving and shooting drills that we had previously started before the call-out. Mind you some of the team members had been working for 13 hours straight. During the training of of the veteran members who had been working the long hours went to holster his Glock .40 after the drill with his finger on the trigger and cranked off a round off into his right leg.
He made a bad mistake,,,thing about it , is that this member was a firearms intructer who harped on firearms safety.
Complacency causes people regardless of training to make mistakes.