Responsibility lies on the person who pulled the trigger; responsibility lies with the guards at the gate who didn’t determine that the Major was armed;
How on earth are you going to stop every armed person going onto FT. Hood? It's a huge base, there are thousands of soldiers who target practice away from their units. hunt, etc.....it is not unusual at all to be armed going onto a military post. Besides, officers are allowed to keep weapons in their on post housing. He didn't necessarily bring the gun onto post with him, it could have already been there.

responsibility lies with the Army itself. Why on earth was this person promoted to Major with all the odd things being noted about him?

The army lost a lawsuit about 4-5 years ago filed by a captain who was bypassed for major.

The end result was that the US Army lost the lawsuit, and was forced to take back a few hundred officers who may or may not have made the cut for promotion without the lawsuit.

Major is almost an automatic promotion, like Sergeant is now. You have to make serious errors to NOT get promoted. Rather than having a competitive promotion system, we're now promoting based on we hope he will do well, rather than we know he will do well. Heaven forbid a senior officer writes a bad OER on someone.......far easier to write a bland generic OER and shuffle them off to their next unit, let them be someone else's headache.

Currently the accountability in the promotion system lies not with the individual, but the people who review the individual. It's HARD to get a bad efficiency report, because it has become a nightmare for the officer or senior NCO who dares to write one.