Well, reportedly there is a spent case on hand from one of the prior shootings, and according to one of the posters above, the weapon has been ID'd as an AK-74 . I assume the FBI knows the difference between a .223/5.56mm case and a 5.45x39mm Russian case.
Of course, if it is truly an AK-74, to me this would increase the likelihood that the shooter is a Middle Easterner or other foreigner, as that is a distinctly unusual weapon in this country. In fact it is a select-fire weapon that was manufactured after the 1968 cutoff for full-auto imports. There shouldn't be any legal weapons of this type in the country, unless owned by police or military. Naturally, they can be had by the barrelful in the arms bazaar of Peshawar.
Does anyone know if there were any semi-auto lookalikes imported?
-ccm
Yes there are, and I believe some are chambered for 5.56 NATO, and I've been told the -74 was designed to chamber the 5.56 NATO for battlefield reasons.