(WASHINGTON) -- A gunman who terrorized the Navy Sea Systems Command headquarters building in Washington, D.C., was shot and killed Monday after carrying out a shooting spree that left at least 12 others dead, according to officials.
Police are also searching for two additional men who are considered "potential" shooters.
The slain shooter was initially described as a former Navy official in his 50s whose work status was recently changed. He was later identified by authorities as Aaron Alexis, a 34-year-old man from Fort Worth, Texas.
"The big concern for us right now is we potentially have two additional shooters," Metropolitan Police Chief Cathy Lanier said.
She said the other two men being sought were wearing military uniforms.
"There is no information to believe they are military personnel, but they are wearing military uniforms," Lanier said.
The chief said one possible suspect was white in a khaki uniform, wearing a beret and carrying a handgun, and the other was described as black man in his 50s wearing an olive drab uniform and carrying a long gun.
Lanier later said at a press conference Monday afternoon that at least 12 people were killed.
President Obama said he had been briefed on the situation and spoke about the shooting at the beginning of a news conference.
"We are confronting yet another mass shooting, and today it happened on a military installation in our nation's capital," he said.
Obama said he wanted a "seamless" investigation into the shooting and is standing with the victims and their families affected by what he called a "cowardly act."
"It targeted our military and civilian personnel, men and women who were going to work, doing their job protecting all of us. They are patriots and they know the dangers of serving abroad," Obama said. "But today they faced the unimaginable violence that they won't have expected here at home."
Two law enforcement officers were among the injured when the suspect fired shots inside the 3,000-person building at 8:20 a.m. Law enforcement officials initially told personnel to evacuate the building but they were later told to shelter in place.
A spokesman for the Bureau of Alcohol, Tobacco, Firearms and Explosives sent a team of special agents to help secure the scene. This is the same team that helped apprehend Boston Marathon bombing suspect Dzhokhar Tsarnaev, according to the spokesman.
At least three gunshot victims were taken to Washington Medical Center with "severe injuries," according to Janis Orlowski, chief medical officer at the hospital.
The victims were described as a male Metropolitan police officer who had "multiple gunshot wounds to his legs," a woman who was shot in the head and the hand, and another woman who was shot in the shoulder.
Orlowski said at least three are in critical condition, however they are conscious and are expected to survive.
The Naval Sea Systems Command, the largest of the Navy's five commands, is responsible for engineering, building, buying and maintaining ships, submarines and combat systems in the Navy's fleet.
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