Possibly his own. If it was a workplace issue, or a personal/domestic issue, often the shooter will commit suicide. In fact, this would be a high probability guess, since (thank the Lord) there hasn't been a report of kids harmed.
"Multiple people, including children, have been killed in a shooting at Sandy Hook Elementary School."
Thank the Lord, just the same. Not one sparrow falls to the ground apart from His will. He knows what He's doing, even when we don't.
Just heard a news report that one suspect (perhaps the dead gunman) was `8 to 20 years old and from New Jersey.