If the question was 'murder or suicide' than I'd say it was likely to be sooner, but I think the combination of "megalomaniac + homicidal + access to printer a

If the question was 'murder or suicide' than I'd say it was likely to be sooner, but I think the combination of "megalomaniac + homicidal + access to printer and plans + access to ammunition + following through" is pretty low. It doesn't really ring true for me either: "first to murder someone with a 3D printed weapon" is only going to appeal to some tiny fraction of the above. Not that it couldn't happen, I just find it too unlikely to really be plausible.