I was interested by the "jams." I'm thinking it was a 3-D printed pistol, which often don't cycle the action properly.

John Wick-style hitmen are pretty rare - I've never even heard of one. Most "hired hitmen" aren't much more than junkies looking for money for drugs. The message on the casings could well be camouflage - why would anyone, amateur or professional, go out of their way to advertise their motive?

Onward and upward,
airforce