WASHINGTON (CNN) -- 8:20 a.m. -- Active shooter is reported inside the Naval Sea Systems Command Headquarters building (Building 197) at the Washington Navy Yard in southeast Washington, according to a statement from the Navy. There is one confirmed injury. A "shelter in place" order is issued for Navy Yard personnel. Several hundred people are evacuated.
9:40 a.m. -- Departing flights are held on the ground at Washington Reagan National Airport; some arriving flights are delayed. The Federal Aviation Administration later said this step was taken to give priority in the airspace around Washington to law enforcement helicopters and other aircraft.
9:50 a.m. -- A Metropolitan Police Department officer is among "several" injured in a shooting at the Navy Yard, according to a D.C. police spokeswoman.
9:56 a.m. -- President Barack Obama has been briefed "several times" about the situation by homeland security and counterterrorism officials.
10:05 a.m. -- U.S. Navy confirms via Twitter several injuries with reports of fatalities.
10:06 a.m. -- Chris Kelly, Metro police spokesman, tells CNN there are 10 victims, including a D.C. police officer and a law enforcement officer moments later described by another official as a base security officer. Kelly tells CNN the main suspect is an adult black male, 6 feet tall, bald head, medium complexion and wearing black clothing - black top and black jeans.
10:26 a.m. -- All flights resume at Reagan National.
10:34 a.m. -- Metro police spokeswoman Saray Leon denies media reports about three suspects possibly involved, saying authorities were looking for one suspect. Repeats 10 victims, but does not confirm fatalities.
10:36 a.m. -- Six public and private schools in the vicinity of the Navy Yard are locked down as a precaution. Two other public and two private schools would also be locked down. The nearby U.S. Transportation Department is also locked down.
10:55 a.m. -- A SWAT team is seen going through the gate at the main Navy Yard entrance. The SWAT team is seen escorting people out of the building where the shooter reportedly is located.
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 special agents.
11:13 a.m. -- Multiple congressional aides from both parties who are involved in intelligence, homeland security and leadership say they have no indication that the attack at the Navy Yard was an act of terrorism.
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, but that those killed were not the two officers who had been shot. Zeigler says law enforcement is still trying to clear Building 197 to determine if there are any more shooters.
11:31 a.m. -- A Navy official tells CNN that Adm. Jonathan Greenart, the top Navy officer at the Navy Yard, was at his residence there when the shooting began. Greenhart was evacuated by secure vehicle, according to the official.
11:38 a.m. -- Janice Orlowski, chief medical officer at Washington Hospital Center, tells reporters at a briefing that her facility has received three gunshot victims -- one male and two females. The male has suffered from "multiple gunshot wounds to his legs," while one of the women was shot in the shoulder and the other was shot in both the head and one hand.
Orlowski says the survival chances for all three victims are "very good."
Orlowski also 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."
11:50 a.m. -- A senior U.S. Navy official tells CNN's Barbara Starr that one shooter is dead. The same official could not confirm there were other shooters, despite Zeigler's prior report that there were two shooters down.
12:09 p.m. -- The Pentagon issues a statement noting that "the Pentagon Force Protection Agency increased its security posture, not out of a specific threat, but as a proactive, precautionary measure related to the ongoing incident at the Navy Yard."
12:14 p.m. -- Metropolitan Police Chief Cathy Lanier says one alleged shooter is deceased, but two other potential shooters are still at large. Lanier says one of the potential shooters still at large is a white male in a tan military uniform, last seen around 8:35 a.m. in possession of a handgun. The other potential shooter still at large is an African-American male approximately 50 years old, last seen wearing olive drab clothing -- a possible military uniform -- and in possession of a long gun.
Lanier says there is no information indicating either of the two alleged shooters still at large are military personnel.
Lanier also notes that "multiple" victims are dead inside the Naval Sea Systems Command headquarters building at the Navy Yard, and that there is still a "very active, ongoing" investigation.
12:20 p.m. -- Dr. Babak Sarani, chief of trauma and acute care at George Washington University Hospital, reports one person dead from a gunshot wound to the head. Victim pronounced dead upon arrival.
12:32 p.m. -- President Barack Obama, speaking on the fifth anniversary of the start of the financial crisis, says he has been briefed the situation at the Navy Yard.
"We still don't know all the facts, but we do know that several people have been shot and some have been killed. So we are confronting another mass shooting and it happened on a military installation in our nation's capital," Obama says.
"It's a shooting that targeted our military and civilian personnel. These are men and women who were going to work, doing their jobs protecting all of us. They're patriots and they know the dangers of serving abroad, but today they face the unimaginable violence that they wouldn't have expected here at home."
Obama called for a thorough investigation.
2 p.m. -- At least 12 people were killed in the shooting, Washington Mayor Vincent Gray said. Metropolitan Police Chief Cathy Lanier said authorities are looking for two additional people who they have reason to believe may have been involved in some way.
2:15 p.m. -- The Senate recessed due to the shooting events.
2:45 p.m. -- D.C. police report one of the people they were looking for -- the white male in a tan uniform -- "has been identified and is not a suspect or person of interest."
3 p.m. -- The Senate goes into "lock down" mode. Nobody is allowed to enter or leave that side of the Capitol due to "uncertainty surrounding the shooting" and particularly the possibility of suspects at large, according to Terrance Gainer, Senate Sergeant at Arms. The Capitol is not far from the Navy.
3:30 p.m. -- The Washington Nationals canceled their game on Monday night due to the shooting, the team said in a statement. Nationals Park is just a few blocks from the Navy Yard.
4 p.m. -- The Washington FBI Field Office tells CNN the dead shooting suspect has been identified by ID and fingerprints as Aaron Alexis, 34, a military contractor from Texas.
4:07 p.m. -- MedStar Washington Hospital Center Chief Medical Officer Janice Orlowski tells reporters that all 3 patients at her facility are stable, and are expected to survive.
4:25 p.m. Mayor Gray said toll rises to 13 dead, and authorities continue to look for potential additional suspect.
6:47 p.m. ET -- Michael Ritrovato, a friend and former roommate of Alexis, told CNN that Alexis was frustrated with the company that contracted him to work for the Navy.
6:54 p.m. ET -- Multiple law enforcement sources say that only one weapon was recovered from the scene of the shooting, CNN's Evan Perez and Pamela Brown report. The sources say the weapon was a "long gun."
7:11 p.m. ET -- Before the shooting, Alexis drove into the naval yard with his military contractor identification card, a U.S. law enforcement official told CNN's Evan Perez.
Alexis, armed with three guns, walked into Building 197, made his way to an overlook above an atrium, and started shooting, the official said.
7:53 p.m. ET -- The wounded Washington police officer who was in surgery today at Medstar Washington Hospital Center was shot multiple times in the legs, and doctors will begin to determine on Tuesday whether he will be able to keep the legs, CNN's Chris Lawrence reported.
8:03 p.m. ET -- In Seattle, police say they arrested Alexis in 2004 for shooting out the tires of another man's vehicle in what Alexis later told detectives was an anger-fueled "blackout."
8:05 p.m. ET -- Adding to what we reported earlier about Alexis' movements (see 7:11 p.m. post) - He entered the facility legally with a valid ID card, a federal law enforcement official told CNN's Susan Candiotti.
Alexis used a legally purchased AR-15 shotgun, according to the official.
8:26 p.m. ET -- About 2,000 people have yet to be released from the Washington Navy Yard after Monday morning's shooting there, though officials hope to let them go in the next three hours, Navy Vice Adm. William D. French told reporters. The military is working with the FBI to process people on the base and release them, and officials are about halfway through the process, French said.
8:27 p.m. ET -- Besides the 13 people who were killed, 14 people were injured in Monday morning's shooting at the Washington Navy Yard, Navy Vice Adm. William D. French told reporters Monday night. The 13 dead include suspect Aaron Alexis.
8:43 p.m. ET -- The Washington police officer who had surgery after being shot in his legs is "alert, he's talkative, and he's doing very well," said Janis Orlowski, the chief medical officer at Medstar Washington Hospital Center.
Earlier, CNN's Chris Lawrence reported that doctors will begin to determine on Tuesday whether he will be able to keep the legs.