A former naval petty officer packing an assault rifle and two other guns sprayed an office building with bullets at the Washington Navy Yard on Monday, killing 12 people in a rampage that paralyzed part of the nation’s capital, authorities said. It was the deadliest mass shooting in the United States since the massacre at Sandy Hook Elementary School last year.

Authorities said that the gunman, a civilian contractor identified as Aaron Alexis, 34, was killed after exchanging fire with officers who stormed the headquarters of the Naval Sea Systems Command in a massive law enforcement response.

Mayor Vincent Gray said there was no information on a motive. Authorities said Alexis might have used someone else’s identification to get into the office building. At least four people were wounded, but some reports placed the number as high as 16.

“There is no question he would have kept shooting,” Washington Police Chief Cathy Lanier said.

Authorities told a late-afternoon press conference that they were still looking for one man considered a possible suspect. Earlier they were looking for two, but they found one and ruled him out as a person of interest, police said.

Besides being the biggest shooting rampage since last December, when 20 children and six adults were killed at Sandy Hook in Newtown, Conn., it was the deadliest on a U.S. military installation since 13 people were killed at Fort Hood, Texas, in 2009.

President Barack Obama called it a “cowardly act.” He said the rampage targeted patriots, military and civilian alike, “men and women who were going to work, doing their job, protecting all of us.”

The Navy said the first shots were fired at 8:20 a.m. ET at the Sea Systems Command headquarters. Alexis was carrying an AR-15 military-style semiautomatic rifle, a double-barreled shotgun and a handgun, law enforcement officials said.

Patricia Ward, who works at the Navy Yard, said she had just gotten breakfast in the cafeteria when she heard “three gunshots, pow-pow-pow, straight in a row.”
“All of the people that were in the cafeteria, we all panicked, and we were trying to decide which way we were going to run out,” she said. “I just ran.”
The roughly 3,000 people who work there were told to stay in place. For the next several hours, conflicting reports circulated about whether the shooter was still alive, whether he had accomplices, how many places were active shooting scenes, and how many people were dead and injured.

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