Re: FBI can't unlock smartphone
There is presumably a small logical difficulty in preventing violent killers in the military having guns
1 this was the Air Force. Very few people in the Air Force have access to small arms, that's not their thing. Honking great nukes, that's different.
2 even in arms of service where a lot of folk have access to small arms, very few have access to them under normal circumstances. Every Marine is a rifleman (even the women) but usually the rifles are locked up. The Army is worse: large chunks of the Army never see a rifle once out of basic training, and same with the Navy, there not being much call for a rifle when you're 300 metres down in a nuke sub or are sitting on an aircraft carrier umty-ump thousand miles from land.
3 the serious head cases tend to gravitate towards the kind of unit where they would have lots of access to small arms. This would tend to put them in units more likely to spend a lot of time out in the bush getting shot at by the head cases on the other side, if they manage to qualify for such units. In many cases they won't, as they often have other problems which disqualify them. The number of violent killers even in gung ho macho special forces units is quite low, and often gets lower when they do something which irritates and/or endangers the others in the unit and they have an unfortunate accident. The military would much rather have the likes of Alvin York or Carlos Hathcock than a violent nutbar.