• 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 motive for the mass shooting -- the deadliest on a military installation in the U.S. since the tragedy at Fort Hood, Texas, in 2009 -- was a mystery, investigators said. But a profile of the lone gunman, a 34-year-old Aaron Alexis, was coming into focus. He was described as a Buddhist who had also had flares of rage, complained about the Navy and being a victim of discrimination and had several run-ins with law enforcement, including two shootings.
• Monday's onslaught at a single building at the highly secure Navy Yard unfolded about 8:20 a.m. in the heart of the nation's capital, less than four miles from the White House and two miles from the Capitol.
• It put all of Washington on edge. Mayor Vincent Gray said there was no indication it was a terrorist attack, but he added that the possibility had not been ruled out.
• "This is a horrific tragedy," Gray said.
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• 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 Monday of the man authorities identified as the gunman in a 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 that 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

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