This is one of those situations where it seems the media is desperate to find something or someone to blame other than the fact that the guy who did the shooting had mental issues, snapped, and the end result was a terribly tragedy.
From what I recall from the billions of different reports (someone feel free to correct anything I've got wrong):
1) He was of legal age to buy and play any games he wanted.
2) He *legally* bought the shotgun in a different state.
3) He had a *government issued* permit to carry a concealed weapon.
4) The pistol he used came from somewhere inside the Naval facility. No AR-15 was involved.
5) He was discharged (not in a bad way, a general discharge) from the military after some run-ins regarding conduct. As is SOP when people leave the military, he would keep his 'secret' clearance level for 10 years.
6) Quite a few people seemed well aware of his PTSD, the voices in his head, and his penchant for violence (shooting through neighbor's floors, shooting out the tires on a car, etc.)
7) He *passed* an in-depth background check to get a job at a contractor who worked for the Naval place
8) He had a legit security badge to get into the facility.
What Fox (and many pundits) seem to have difficulty with is that the vast majority of events leading up to this were perfectly legal, including the purchase of the shotgun, and normal. He passed background checks on multiple occasions. The one huge clue that seemed to be overlooked was the PTSD, the anger, and the voices, but when he snapped that could have just as easily resulted in him driving his car off a cliff or jumping out of a window. Sadly, what he did was far more horrific.
In hindsight it's easy to say, "oh well, he shouldn't have been allowed a gun or video games because he was a nutcase," but the reality is that his friends and colleagues would never even dream that he'd do something like this, because you never think that your friends and family are capable of such atrocities. That's human nature.
In an ideal world, he would have been encouraged to see someone about his mental problems, but it didn't happen and, instead, his friends enabled his irrational behavior and addiction by doing things like not kicking him out when it came to dinner time and, instead, feeding him so he could carry on gaming.
The person to blame is dead, so the media want something tangible to blame in his place.