You may want to get your facts straight. The Federal ban in 1994 specifically notes a detachable magazine and 2 or more of the features to classify it as an assault weapon under the ban. Listed are "pistol grip, folding or telescoping stock, bayonet mount, flash hider or threaded barrel to accommodate one, and grenade launcher. This effectively banned all AR rifles at the time on the merit of just features alone and in addition the law specifically names Colt, Kalashnikov and FN and some lesser names as models banned from sale.
Regardless of the media's motives, all mass shootings are being reported long before the type of firearm has even been disclosed so I'm not sure why you're insinuating it's only reported when it's a semi-auto rifle. Pay attention, the reason the Michigan State incident has less coverage is based on race, as are the gang related incidents and that's all I'll say on that.
And please don't accuse me of twisting anything to suit whatever needs you think I have. It was a very basic post on what has led to why people are using AR's to carry out mass shootings and not a bolt-action rifle.