Considering they were all pig-piled on top of him and beating him right before the execution, for no reason other than “it’s fun!”, I’m not the least surprised at this. ICE are violent sociopaths, overjoyed at being allowed to employ lethal violence whenever they choose (and no doubt being encouraged to do so), and they were celebrating the “kill” they’d just made.

It’s obvious from the fact that they unloaded on his body even after the victim was dead that they all wanted nothing more than to beat and shoot someone, and well, shit, even if the guy is dead already, you’d can at least riddle his body with bullets and get 90% of the feeling of having murdered someone. Even if you didn’t actually file the lethal shot it’s still a rush, and better luck next time when you might be the one, the first guy to pull the trigger, can’t wait!

I wouldn’t be surprised to see them breaking out the beers and partying after a kill. That is, after relieving the victim’s corpse of their wallet, phone and other valuables of naturally.