Police were called to the facility at about 11 p.m. local time for what has become the country's deadliest shooting since 10 people were killed March 22 at a grocery in Colorado.

The coroner's office had yet to officially identify any of those killed as of late Friday morning. Investigators are trying to determine the motive and were searching what they believe is the gunman's home, FBI special agent in charge Paul Keenan told reporters late Friday morning.