10:34 a.m. -- Metro police spokeswoman Saray Leon denies media reports about three suspects possibly involved, saying authorities were looking for one suspect.
10:40 a.m. Counterterrorism officials have briefed President Barack Obama "several times" about the shooting, a White House official says.
10:46 a.m. At least 10 people have been injured, according to police. Navy issues statement saying there are "several injuries with reports of fatalities."
10:55 a.m. -- SWAT team moves through main gate and helps get people out of the building.
11:07 a.m. -- Law enforcement official reports the federal Bureau of Alcohol Tobacco, Firearms and Explosives emergency response team is sent to the scene. It is the same one that helped Boston police apprehend Dzhokhar Tsarnaev. The official notes the team includes approximately 20 specially trained, locally stationed agents.
Confusion over shooters
11:29 a.m. -- Ed Zeigler, Director of Public Affairs for Naval District Washington, tells CNN two shooters "are down" at the Navy Yard. Zeigler cannot confirm if the shooters are in custody or dead.
Zeigler also tells CNN there have been "multiple deaths" at the Navy Yard. Zeigler says law enforcement is still trying to clear Building 197 to determine if there are any more shooters.
11:31 a.m.: Helicopter hover over the scene, and it appears one chopper contains a police sniper.
11:50 a.m. -- A senior Navy official tells CNN's Barbara Starr that a suspected shooter is dead.
The suspect was identified as Aaron Alexis, 34, a former Navy reservist and a current military contractor, the Washington FBI Field Office told CNN. His identity was confirmed by fingerprints and a picture ID card.
11:38 a.m. -- Janice Orlowski, chief medical officer at MedStar Washington Hospital Center, notes that the weapon used to shoot the victims "had to be a semi-automatic because they're talking about gunshots that they heard in rapid succession."
12:14 p.m.: Police say they are looking for two other possible suspects. One was described as a white male in a khaki tan military uniform with a handgun. Authorities also were on the lookout for a black male, about 50, who may have had a long gun. That person was wearing an olive, drab colored, possible military style uniform, Lanier said.
The white male was later cleared of any involvement, while the search continued for the second man, authorities said.
2 p.m.: Washington Mayor Vincent Gray said 12 people were killed. He later added a 13th fatality, including the main suspect.
7 p.m.: FBI investigators rule out additional shooters but Metropolitan Police still sought one person to discern if there was any involvement.