I think the guy may have been on the run for awhile going room to room shooting.
Probably. It will probably take a day or so to get the actual sequence of events. With these kinds of situations rumors fly like wild.
In one of the on-line news phone interviews with one of the wounded, one of the surviving witnesses said the shooter opened the classroom door, emptied the magazine, and then slammed the door.
In another, he reportedly lined his victims up in a row, then went down the line executing them.