3D printed handgun is just so gay and impossible. to be anything decent you would need to buy most of everything other than the frame. i would just buy a gun or make one out of a piece of pipe.
I'm positive he didn't print one of these:
In addition to that being one shot (and the article claims he "pumped bullets" into the victim), I'm also positive he wouldn't be smart enough to 3D print anything. I guess it's remotely possible he acquired a frame that was 3D printed by someone else. I'll wait until they prove that with evidence though. A P80 as suggested earlier is still where I'd place my bet on.