still...we don't know for sure but I figured the odds were greater that this is what he had instead of true full auto whether made from the factory full auto or converted by himself into full auto.

Used to be the AR-15 could be converted to full auto by purchasing a full auto sear(probably just a M-16 sear) that you could pick up at the gun shows for a song and a dance. You could have the AR-15 and the sear but you couldn't have the AR modified(drilling one or two hole in the receiver) to utilize the sear. My understanding is, and I don't know where the break is in model year, the newer model AR's have been made to where it's very difficult, if not impossible, to modify to full auto.

To get around all of this, as the gun world is apt to do, they made something called a bump stock. It's a little hard to splain...so a video link below. Simple pimple and she aint hard to look at...starts about 2.08. Prior to that shows her converting it...very simple process.