WASHINGTON (AP) -- The deadly attack at the Washington Navy Yard was carried out by one of the military's own: a defense contract employee and former Navy reservist who used a valid pass to get onto the installation and started firing inside a building, killing 12 people before he was slain in a gun battle with police.
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.
D.C. Police Chief Cathy Lanier says investigators now believe Alexis acted alone. Authorities had earlier said they were searching for a possible second suspect.
Investigators say his motive is a mystery.
Gunman in Navy Yard shooting was in Navy Reserves
Aaron Alexis seems a study in contradictions: a former Navy reservist, a Defense Department contractor, a convert to Buddhism who was taking an online course in aeronautics. But he also had flashes of temper that led to run-ins with police over shootings in Fort Worth, Texas, and Seattle.
A profile began to emerge of the man authorities identified as the gunman in Monday's mass shooting at the Navy Yard in Washington, D.C., that left 13 people dead, including the 34-year-old man. While some neighbors and acquaintances described him as "nice," his father once told detectives in Seattle his son had anger management problems related to post-traumatic stress brought on by the terrorist attacks of Sept. 11, 2001. He also complained about the Navy and being a victim of discrimination.
Police in Seattle say Alexis was arrested there in 2004 for shooting out the tires of another man's vehicle in what he described to detectives as an anger-fueled "blackout."