He failed the background check back in 2014. I have not seen when he purchased the rifle. It could have been years ago.
Not knowing when that purchase was made, it could have even antedated the failed background check.
Unfortunately, these incidents are each building toward the aims of the anti-gun cadre:
Banning AR and other semiauto rifles.
Banning magazines which hold more than
X cartridges,
X being some arbitrary number far less than the standard magazines these firearms were designed to use.
Ending lawful private sales without documentation and background checks.
Ultimately, Red Flag laws, registration, and confiscation.