5:08 p.m.: The Fort Worth Star-Telegram reports that shooting suspect Aaron Alexis was arrested in 2010 for allegedly shooting his handgun into the ceiling of his apartment in Fort Worth, Texas. The woman told police that she was "terrified" of Alexis and that he had called the police on her several times over noise complaints.
Friends told the Star-Telegram that he left his job as an aviation electrician's mate in the Navy Reserve "because he didn't like to get up early and had complained about getting underpaid" and eventually became a waiter and deliveryman at a restaurant called Happy Bowl Thai in Forth Worth.
Nutpisit Suthamtewakul, owner of Happy Bowl Thai, told the Star-Telegram that Alexis was his "best friend" and said, "He didn't seem aggressive to me."
4:51 p.m.: ABC News reports that Alexis had military ties:
The FBI is asking anyone with information about Alexis to call 1-800-CALL-FBI.
4:27 p.m.: Valerie Parlave, assistant director in charge of the Washington, D.C., field office of the FBI, confirmed that the deceased shooting suspect has been identified as 34-year-old Aaron Alexis of Fort Worth, Texas.
Mayor Vincent Gray put the death toll at 13 fatalities, including Alexis. In response to questions about whether this was an act of terrorism, Gray told reporters, "We don't know what the motive is at this stage."
D.C. Metropolitan Police Chief Cathy Lanier called it "an ongoing investigation" and confirmed that Alexis died in a shootout with police.
4:11 p.m.: Dr. Janis Orlowski of MedStar Washington Hospital tells reporters that the three shooting victims taken in by the hospital earlier are in stable condition and are expected to recover. Two of them, the D.C. Metro Police officer and a female civilian, are still in surgery.
3:41 p.m.: The AP reports that the suspected gunman, Aaron Alexis, is believed to have a criminal record and a concealed carry weapon permit. An official tells AP that Alexis was able to gain access to the Navy Yard with someone else's ID card. Alexis was one of the 12 people who died at the scene of the shooting.
Today's Major League Baseball game in D.C. between the Washington Nationals and the Atlanta Braves has been postponed. The teams will play a double-header on Tuesday instead.
3:16 p.m.: Multiple news outlets have identified the shooting suspect:
The Senate Sergeant of Arms, according to The Washington Post, has told all Senate staffers that nobody is allowed to enter or leave any of the Senate buildings for the next two hours "out of an abundance of caution."
2:49 p.m.: Police have stopped looking for one of the shooting suspects, described as a white male in a tan, military-style outfit:
Police are still for looking for the other suspect, described as a black male in an olive, military-style uniform.
2:13 p.m.: D.C. Metropolitan Police Chief Cathy Lanier put the number of fatalities at 12 and claimed that police were still looking for the two additional shooting suspects, one described as a white male with a tan, military-style uniform and a beret-style hat, the other a black male wearing an olive military-style outfit.
She also said that the FBI is taking the lead in the investigation.
1:27 p.m.: And now doubt has been cast on whether or not there was more than one shooter:
12:58 p.m.: The death toll is now seven, which includes the gunman, reports The Washington Post.
A previous report that one of the shooters had been identified has been retracted by CBS News.
12:51 p.m.: The death toll remains a matter of some dispute.
12:41 p.m.: D.C. Metropolitan Police are asking for any tips on the shooters:
Police are looking for two shooting suspects who may still be at large. Both were reportedly wearing military-style uniforms. Another gunman has been reported dead.
12:37 p.m.: President Barack Obama called the shooting a "cowardly act."
"We are confronting yet another mass shooting," the president said. "And today it happened on a military installation in our nation's capital." The victims, Obama said, were "men and women who were going to work, doing their job, protecting all of us. They are patriots. They did not expect to be attacked at home while in their offices."
12:20 p.m.: "We have one shooter who we believe was involved with this that is deceased," said D.C. Metropolitan Police Chief Cathy Lanier at a press conference. "We potentially have two other shooters that we have not located."
The two other shooting suspects were described as a white male wearing a khaki, military-style uniform last seen carrying a handgun around 8:30 a.m., while the other was a black male, approximately 50 years old, who was reportedly seen carrying a long gun and wearing an olive, collared military-style uniform.
"We have no reason to be believe they are military personnel," stressed Lanier.
12:04 p.m.: The AP reports that six people were killed in the shooting.
11:50 a.m.: Dr. Janis Orlowski tells reporters that MedStar Washington Hospital has taken in three gunshot victims, who were alert enough to describe their experiences, all of which made it sound like the gunman or gunmen used semi-automatic firearms.
Two of the victims being treated are female civilians, while the other is a D.C. Metro Police officer. All of their "chances for survival are very good," said Orlowski during a press conference.
NBC News reports that a shooter is dead:
Terry Durham, a woman who claimed to be a witness to the attack, tells The Washington Post that a man walked down a hallway with a rifle and shot at them.
"He was tall," she said. "He appeared to be dark-skinned."
Witnesses also described a gunman shooting down from the third or fourth floor of a Navy Yard building into the first-floor cafeteria.
While details about the shooter or shooters are scarce, NBC News's Pete Williams reports that the dead gunman had access to the Navy Yard:
11:12 a.m. EST: CBS News correspondent David Martin reports that at least three people, and as many as six, have been killed in the shooting. CBS reports that it is still an "active shooter scene."
D.C. police now believe there are two shooters, including one wearing fatigues, according to The Washington Post. One gunman is "down," while the other has been pinned down between the third and fourth floors of one of the Navy Yard buildings.
Officials tell the Post that a D.C. Metro Police officer was shot twice in the leg and had to be evacuated by helicopter.
Flights resumed at Reagan International Airport at 10 a.m. after initially being delayed by the Federal Aviation Administration. Six schools in the area have been put on lockdown, meaning visitors and staff are not allowed to enter or leave the building.
10:45 a.m. EST: Four people are dead after at least one gunman opened fire at the Navy Yard in Washington, D.C., on Monday morning, reports NBC News.
That number was confirmed by Ed Buclatin, the public affairs chief for the Navy Installations Command.
From there, details get a bit contradictory and unclear. Police at the scene have reported that three people were involved in the shooting. One is "down," police tell The Washington Post, but two remain at large within the building. A Navy spokesman couldn't confirm that there where multiple gunmen involved.
Initial accounts of the incident cited only a single gunman.
Witnesses first reported hearing shots at 8:20 a.m. at the Naval Sea Systems Command Headquarters, which houses around 3,000 employees. Staffers tweeted photos from the scene: