Leaving aside the horrific act and just looking at it unemotionally for a second.
I can’t work out what the hell he was thinking? Pretty sure a Police officer with their service issued pistol is subject to stringent audit requirements regarding that weapon and any ammunition issued.
For example, I wouldn’t have thought you can just fire off a few rounds in your spare time, without that being picked up and hence, getting probed and reprimanded over the unaccounted for ammo. Or even lose/misplace a few rounds. Hence you probably wouldn’t get away with firing off a few rounds from your service pistol at cans by the camp fire for *smile* and giggles over a few beers with your mates, any more than you would using the said pistol to murder people.