Until an empty case is found we won't know which cartridge was used. My understanding is that a .223 case (5.56x45) was found at the site of one of the first round of shootings in Rockville. Now, did that come from the perp's rifle, or was it a red herring?
I even wrote that on one of the threads but people are still questioning it so I don't know if it's true or not. That fact seems to have gone away from the threads.