Does America need the law of the jungle - the second amenemnt to the US Constitution?

Texas shooting: Gunman Devin Kelley 'had row with mother-in-law' http://www.bbc.com/news/world-us-canada-41892838 So, a deranged man had row with his mother-in-law, and he could buy guns to kill 26 people in a church! And, how did this court-martial convicted criminal buy those weapons? None of his criminal records apparently came up on his 'instant background check when he sought to buy firearms from a sporting goods store in Texas'. He 'also did not disclose details of his military criminal justice record on his purchase paperwork'. So, the gun ownership disgrace of the USA is too eager to allow people to buy guns with the silly instant background check, and relies on criminals to reveal their criminal records!!
Well, arguments with in-laws can hardly be considered grounds for mental illness, lol. Now it appears USAF neglected] to enter discharge info into government database, wtf. Row with someone is not necessarily mentally sick, but his overall background was not mentally healthy enough to be allowed to have guns. A comprehensive background check would have revealed that.Clearly. It was an error on the part of USAF, they seem to be accepting responsibility for their negligence.