The rifles were bought from a Federal Firearms Licensee and there was 100% a background check done.
All online sales that cross state lines must go through a FFL and an FBI NICS check is required to be done before the firearm can be sold. Requiring all mental health diagnoses to be entered into a database that can restrict one's constitutional rights will not do much but prevent people from seeking help. This happened with the VA a few years ago.
Very simple question if something is going to violate the Constitution, would a similar edict on any of the other Constitutional rights be acceptable to you? If we required a civics class with a passing grade and working knowledge of how government works to vote would that be acceptable to you? And yes, requiring someone to be licensed to have arms in the US is a violation of the Constitution. See District of Columbia V Heller and McDonald V City of Chicago.
Some do argue exactly that. There are some that argue anything the government is allowed to have is comething the citizenry should have access to as well. Hunting has absolutely nothing to do with the second amendment. The entire purpose of the second amendment is to prevent governmental tyranny. You want gun owners to buy in to giving up standard capacity magazines and semi automatic rifles, take them away from the government and it's agent's first.
Apply that to other rights and see where it gets you. The easiest one is the first, does that only apply to a box in the town square and the printing presses of the time? And no, the musket was not the most complex firearm of the 1700's, there were semi automatic and fully automatic firearms available. The musket was just the most common.
If he had been "involuntarily committed" that would have made him a prohibited person. If the state had given that information to be included in NICS. This is the route that really needs to be explored, and not giving 4th, 5th and 6th chances.
Agree that there is a profile. A couple of things I think could be done while maintaining Constitutionality and keep firearms out of the hands of kids like this. Add animal abuse to the list of disqualifying crimes. Add juvenile records to NICS with a change that disqualifying crimes includes those crimes that would be disqualifying if committed by an adult. Put teeth into the law that requires the states to put their acts into NICS. Many prohibited persons have been able to get guns after moving states because the states didn't update NICS. Use the civil commitment process. This is the only way to take away someone's rights without a criminal conviction.
Stop comparing getting a gun to getting an abortion, or I've seen some memes comparing it to buying pseudoephedrine. Especially when you have absolutely no idea the process to legally purchase a firearm.
Make schools a harder target. Allow those with carry permits or those that are willing to take up that mantle to protect schools in the same manner we protect everything else. If I go to my state capitol or school board meeting there are folks with guns there to protect the politicians, why not let those that have been through the background checks and training to protect the kids? Not necesarily police since we saw how that worked out in Parkland, but mothers, fathers and staff inside the schools.