Update 3:39 p.m.: Federal law enforcement officials say the man accused in a shooting rampage at the Washington Navy Yard that left at least 12 people dead has been identified as Aaron Alexis.
The two officials spoke Monday to The Associated Press on condition of anonymity because they were not authorized to speak publicly.
One of those officials says Alexis was a 34-year-old from Texas. He is believed to have a criminal record there and to be a holder of a concealed carry weapon permit.
That official says Alexis is believed to have gotten into the Navy Yard by using someone else's identification card. It is not yet clear if that individual was an accomplice or if that person's ID card was stolen.
Note: To hear the 3 p.m. interview with WAMU's Patrick Madden, click the play button below the headline at the top of the page.
Update 2:56 p.m.: Police say a man in a tan, military-style outfit who had been sought in connection with the shooting rampage at the Washington Navy Yard has been identified and is not a suspect or a person of interest in the slayings.
Update 2:16 p.m.: Police say at least 12 people have died in the shootings at the Washington Navy Yard.
D.C. Police Chief Cathy Lanier said during a news conference Monday that 12 people were confirmed dead.
Lanier says people are being told to stay in their homes and out of the area as authorities search for two other possible suspects. One of the shooters has died.
The police chief says officers are searching for two other people with firearms wearing military-style uniforms.
She says there is no indication of a possible motive at this time.
Update 1:45 p.m.: As many as three gunmen opened fire Monday inside one of the Navy's oldest buildings, attacking office workers at a heavily guarded military facility in the heart of the nation's capital. At least six people were killed.
One of the gunmen was dead, and police were searching for two other men believed to have joined in the attack at the Washington Navy Yard. The suspects were reportedly dressed in military-style clothing, including one who had on a beret.
In all, more than a dozen people were shot, at least half of them fatally. It was not immediately clear whether that number included the dead gunman.
The attack unfolded just a short distance from the White House and the U.S. Capitol at a former shipyard that is one of the Navy's oldest shore facilities.
The building that was targeted was the military's headquarters for Naval Sea Systems Command, which buys, builds and maintains ships, submarines and combat systems. About 3,000 people work at the headquarters, many of them civilians.
Witnesses described a gunman opening fire from a fourth-floor overlook, aiming down on people in the first-floor cafeteria. Others said a gunman fired at them in a third-floor hallway.
It was not clear whether the witnesses on different floors were describing the same gunman.
As emergency vehicles and law enforcement officers flooded streets around the complex, a helicopter hovered overhead, nearby schools were locked down and airplanes at nearby Reagan National Airport were briefly grounded so they would not interfere with law-enforcement choppers. Less than 2 miles away, security was beefed up at the Capitol and other federal buildings, but officials said there was no known threat.
President Barack Obama mourned yet another mass shooting in the U.S. that he said took the lives of American patriots. Obama promised to make sure "whoever carried out this cowardly act is held responsible."
Two Navy officials confirmed at least six people had died. The officials spoke on condition of anonymity because they were not authorized to talk about the situation publicly.
Todd Brundidge, an executive assistant with Navy Sea Systems Command, said he and other co-workers encountered a gunman in a long hallway on the third floor. The gunman was wearing all blue, he said.
"He just turned and started firing," Brundidge said.
Terrie Durham, an executive assistant with the same agency, said she also saw the gunman firing toward her and Brundidge.
"He aimed high and missed," she said. "He said nothing. As soon as I realized he was shooting, we just said, `Get out of the building."'
Rick Mason, a civilian program-management analyst for the Navy, said a gunman was shooting from the overlook in the hallway outside his office.
Shortly after the gunfire, Mason said, someone on an overhead speaker told workers to seek shelter and later to head for the gates at the complex.
Patricia Ward, a logistics-management specialist, said she was in the cafeteria getting breakfast.
"It was three gunshots straight in a row - pop, pop, pop. Three seconds later, it was pop, pop, pop, pop, pop, so it was like about a total of seven gunshots, and we just started running," Ward told reporters several blocks away from the Navy Yard.
Ward said security officers started directing people out of the building with guns drawn.
One person died at George Washington University Hospital of a single gunshot wound to the left temple, said Dr. Babak Sarani, director of trauma and acute care surgery. A police officer and two civilian women were in critical condition at Washington Hospital Center, said Janis Orlowski, the hospital's chief operating officer.
Orlowski said the police officer was in the operating room with gunshot wounds to the legs. One woman had a gunshot wound to the shoulder. The other had gunshot wounds to the head and hand.
Update 12:48 p.m.: President Barack Obama is mourning what he called "yet another mass shooting" in the United States that he says took the life of American patriots. Obama promised to make sure "whoever carried out this cowardly act is held responsible." The Washington Navy Yard is about 3 1/2 miles from the White House.
Update 12:36 p.m.: Authorities say they are looking for two additional suspects in the shooting rampage at the Washington Navy Yard. District of Columbia Police Chief Cathy Lanier says witnesses reported seeing two additional gunmen, both dressed in military-style clothing.
Update 12:03 p.m.: Navy officials say at least 6 people are dead in the Navy Yard shooting.
Update 11:37 a.m.: A federal law enforcement official says the shooter at the Washington Navy Yard has died.
Update 11:07 a.m.: Officials say police are looking into the possibility of a second shooter at the Navy Yard where several people have been reported killed.
Update 10:30 a.m.: President Barack Obama is getting frequent briefings on a deadly shooting at the Washington Navy Yard.
10:25 a.m. via AP: A Defense Department official says several people have been killed and as many as 10 have been wounded in a shooting at the Washington Navy Yard.
The official spoke on condition of anonymity Monday because the official was not authorized to discuss the matter publicly.
The official also says the shooter is "contained" but not yet in custody.
Earlier in the day, the U.S. Navy said it was searching for an active shooter at the Naval Sea Systems Command headquarters, where about 3,000 people work.
The exact number of people killed and the conditions of those wounded was not immediately known.
- Michelle Boorstein, reporter for The Washington Post. She tweets @mboorstein.
- Patrick Madden, reporter for NPR member station WAMU in Washington, D.C. He tweets @Patrick_Madden.
- Carrie Johnson, justice correspondent for NPR. She tweets @johnson_carrie.
- Sami Yenigan, producer for NPR. He tweets @Sami_Yenigun.
This segment aired on September 16, 2013.