The gunman was a man, named in media reports as Adam Lanza. HE killed his mother then drove to the school and killed six adults, all women, with a rifle before taking his own life. Eight boys and twelve girls were also killed - all but four were aged below six. When the teachers heard the gunfire, they immediately locked the doors and ushered the children into closets in order to protect them.
I think the gunman must be unfit psychologically to kill his own mother