Unless this was an EXTREMELY defective S&W, then it didn't "go off" because he hit the slide release or the safety. Something contacted the trigger. Also, wouldn't the slide be in battery before he started to re-holster? So the "slide release" part really makes no sense. Hopefully this LEO was just badly misquoted.“He was trying to place it back in the holster and somehow hit the slide release or the safety and it actually went off,” Guadalupe County Sgt. Donny White said.
The gun was a 9 mm Smith & Wesson, White said.
I'm wondering whether this might have been an IDPA or USPSA event. I know my IDPA club really stresses safety when reholstering your loaded weapon, since there is zero concern about timing on that part.