[Updated at 12:27 p.m. ET] The mom who spoke to CNN's Meredith Artley said she heard "at least 100 rounds" being fired.
The shooting began about 9:35 a.m., the parent said. There was a "pop pop pop" in the hall outside the room. Three people went out of the room into the hall where the sounds had come from. "Only one person came back," we were told.
The witness told Artley that she then called 911. She said she never saw the shooter but she later was escorted outside the room past two bodies lying in blood.