Motive A Mystery In Navy Yard Mass Shooting

WASHINGTON (AP) — Investigators say the motive for Monday's mass shooting at Washington Navy Yard remains a mystery.

After law enforcement officers spent much of the day Monday looking for other possible gunmen, police now say they "feel comfortable" that the shooter acted alone.

He's been identified as Aaron Alexis, a 34-year-old defense contract employee and former Navy reservist. Twelve people were killed before police shot Alexis to death.

The shooting was the deadliest on a military installation in the U.S. since the tragedy at Fort Hood, Texas, in 2009.

Law enforcement officials say gunman Aaron Alexis carried three weapons at the Navy Yard: an AR-15 assault rifle, a shotgun and a handgun he took from an officer at the scene.