Ruger .44 Carbine, Security-Six, Service-Six, Mini-14, .30 Carbine Blackhawk
If I have learned anything from watching Perry Mason, it's to never pick up a firearm that lying on the ground.News account indicates that the civilian picked up the shooter’s AR after shooting the bad guy with a handgun. The shooter had retrieved the rifle from his car after fatally shooting a police officer with a shotgun.
Seeing an unknown person holding an AR, the responding LEO did the logical thing, sadly.
I wasn't there and I dunno exactly what happened, but honestly,
there would be no reason for the guy to pick up that rifle.