Is there some information they are keeping secret about the recovered bullets?
I thought that same bullet diameter (0.224") was shared with the;

219 Zipper
222 Remington
22 PPC
222 Remington Magnum
225 Winchester
224 Weatherby Magnum
22-250 Remington
220 Swift

I want to know the truth.  Can they prove it is a 223 Rem/5.56mm or are they taking out of their ass as usual?

Has anyone heard anything about this?

They are saying that is might either be a Colt Hbar or a Ruger Mini-14. My best guess is that they have determined from recovered bullets that the rifling twist of the rifle is 1 in 7, which is only shared by the Colt or early model Ruger Mini-14's. It also match probably millions of military M16 rifles!

Who is saying that it matches a AR-15 or a Mini 14?

They found a case, he left one with the tarot card. So apparently it is .223 Rem. There are still a lot of rifle chambered for that.

That case could still be a throw down.

Judging the way this/these serial killer is operating any evidence left at the scene could be salt.

Possible, but he left some more incriminating stuff behind-like his handwriting on the tarot card. And the only point of leaving anything behind is to tease the police. Neither piece of evidence is any good unless they catch him. He probably really did leave one of his own cases behind so the cops would not mistake another persons rifle for him and he would get all the credit not a copy cat or a innocent person.

They also have 6 (now 7, according to the news) bullets (or fragments thereof) left in the bodies of the victims.

As for the gun, most of the 1:7 twist ARs I've seen were 'target' models... Most of the regular HBAR A2 clones that I've seen are 1:9..

The bullets aren't going to tell you if its a self loader or not.

Unless none of the bolt rifle builders use 1 in 7 twists on their .223 barrels. Any twist between 1in8 and 1in12 could be either a self loader or a bolt.

The rounds you mention all sound like possibilities.  It sure seems like this person would be using a bolt gun and not an auto loader.  I have heard that the suspect is being profiled as having a military or police training background.  Wouldn't a military guy use a .308?  Doesn't Law enforcement also use 30 caliber?

Some guys at work were discussing this, and one said it had to be an AR15 because it was a 223. I then started rattling off the different calibers that used the same diameter bullet, and the different makes/ models of rifles that fired these bullets.
He then said that they had found a case--I told him that anybody could pick up a case at a range to drop at the scene.
He then said it has to be a guy with sniper training because of the accurate shots--I told him that competition shooters, deer hunters, varmint shooters, etc. all practice firing one accurate shot, and that the shooter isn't making any really spectacular shots anyway.