All of them fire NATO 5.56 (nearly identical to Remington .223) ammunition.
However, all of these rifles except for the Commie-made "AK-74" are uncommon in the US -- even during the public 'Assault Weapons' buying spree of the late 1980s/early 1990s. The South African R4 is almost never seen.
I would expect that if the shooter really is using an "AK-74", that it's a Romanian clone or a recent Russian 'sporterized' import chambered in Remington .223.
It's just my opinion, but I don't think that anyone who's got a fascination with the 'Sniper Culture' would choose an AK-74 for their rifle.
But an arab terrorist (who are not known for their military minds) might. They might want to stick with something they are familar with.
It is most likley just the media that is fascinated with the sniper culture rather than the killer. He may have an illegal ak-74 or may have bought a semi-auto version simply because that is a rifle that he is familiar with. Which would be the case if we are talking about a terrorist trained in the middle east.
I used to own a Valmet M76 in .223. It was one of the best made AKs I ever handled; ignoring the horrid ergonomics, it was actually an AK design that felt like it had been designed with the shooters in mind. And while not particularly accurate compared to an AR15, it was very accurate for an AK action. It could do 1.5 MOA all day with decent ammo.
