WASHINGTON — A defense contractor went on a shooting rampage Monday inside a building at the heavily secured Washington Navy Yard, spraying bullets in the hallways and firing from a balcony onto workers in an atrium below. Thirteen people were killed, including the gunman.
Police said the gunman, 34-year-old Aaron Alexis of Texas, used a valid pass to get onto the base before launching the attack, which 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.
Alexis died after a running gunbattle inside the building with police, investigators said.
"This is a horrific tragedy," Mayor Vincent Gray said.
Investigators said the motive was a mystery. The mayor said there was no indication it was a terrorist attack, but he added that the possibility had not been ruled out.
For much of the day, authorities said they were looking for a possible second attacker who may have been disguised in an olive-drab military-style uniform. But by late Monday night, they said they were convinced the attack was the work of a lone gunman, and the security lockdown around the area was eased.
"We do now feel comfortable that we have the single and sole person responsible for the loss of life inside the base today," Washington Police Chief Cathy Lanier said.
It was the deadliest shooting at a military installation in the U.S. since Maj. Nidal Hasan killed 13 people and wounded more than 30 in 2009 at Fort Hood in Texas. He was convicted last month and sentenced to death.
President Barack Obama lamented yet another mass shooting in the U.S. that he said took the lives of American "patriots." He promised to make sure "whoever carried out this cowardly act is held responsible."