He claimed he unloaded it and checked he unloaded it.
A couple weeks later every single one of those guns was recalled and replaced by the manufacturer. The gun, itself, apparently had a defect wherein it could pop a round loose, hold it where you couldn't see it, and then chamber it if you knocked it a bit. I have no idea how this could possibly occur, but the manufacturer actually claimed this and wound up having to spend enough money that something wasn't right with those handguns.
Fortunately, he adhered to standard discipline and made sure the gun was never pointed at anybody. So, when it did go off, nobody was in line of fire. However, it did ricochet and still could have caused quite a bit of harm.
Always adhering to discipline doesn't make probabilities zero--it just minimizes them.
My military-trained father-in-law accidentally discharged his handgun inside the house while cleaning it. The bullet ricocheted and could have killed anybody.
It was a manufacturing defect. All those guns were recalled and replaced 2 months later.