"He was explaining that the magazine that fits the full-size Smith & Wesson also fits the subcompact," Wilber said. "He was juggling the magazine between the guns and had a gun in each hand and his duty weapon discharged."The weapon discharged... all on its own. Not that he actually fired the weapon.
There are some simple rules of handling guns. Juggling doesn't fall in there as a method of safe handling. He didn't keep the weapon pointed in a safe direction. He didn't unload the weapon that was not in use. He didn't keep his finger away from the trigger. He did act like and idiot.
I am sure he feels bad. (He will feel worse after reading everything that everyone will write about it.) He should still face something like a suspension, or worse.