Police officer killed by driver who rammed barricade outside US Capitol building named

The Capitol police officer killed by a man who rammed a car into him and another officer at a barricade outside the US Capitol and then emerged wielding a knife has been named.

It was the second line-of-duty death this year for a department still struggling to heal from the January 6 insurrection.

Video shows the driver of the crashed car emerging with a knife in his hand and starting to run at the pair of officers, Capitol Police Acting Chief Yogananda Pittman told reporters.

Authorities shot the suspect, who died at a hospital.

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Two law enforcement officials told The Associated Press that the suspect stabbed one of the officers.

The officials spoke to AP were not authorised to publicly discuss the pending investigation and spoke on condition of anonymity.

"I just ask that the public continue to keep US Capitol Police and their families in your prayers," Acting Chief Pittman said.

"This has been an extremely difficult time for US Capitol Police after the events of January 6 and now the events that have occurred here today."

Police identified the slain officer as William "Billy" Evans, an 18-year veteran who was a member of the department's first responders unit.

Authorities said that there wasn't an ongoing threat and that the attack did not appear to be related to terrorism, though the Capitol was put on lockdown as a precaution.

There was also no immediate connection apparent between Friday's crash and the January 6 riot.

The crash and shooting happened at a security checkpoint near the Capitol typically used by senators and staff on weekdays, though most are away from the building during the current recess.

The attack occurred about 91 metres from the entrance of the building on the Senate side of the Capitol.

One witness, the Reverend Patrick Mahoney, said he was finishing a Good Friday service nearby when he suddenly heard three shots ring out.

It comes as the Washington region remains on edge nearly three months after a mob of armed insurrectionists loyal to former President Donald Trump stormed the Capitol as Congress was voting to certify Joe Biden's presidential win.

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Five people died in the January 6 riot, including Capitol Police officer Brian Sicknick, who was among a badly outnumbered force trying to fight off insurrectionists seeking to overturn the election.

Authorities installed a tall perimeter fence around the Capitol and for months restricted traffic along the roads closest to the building, but they had begun pulling back some of the emergency measures in recent weeks.

Fencing that prevented vehicular traffic near that area was recently removed.

Law enforcement officials identified the slain suspect as 25-year-old Noah Green.

Investigators were digging into the suspect's background and examining whether he had any mental health history as they tried to discern a motive.

They were working to obtain warrants to access his online accounts.

Pittman said the suspect did not appear to have been on the police's radar.

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But the attack underscores that the building and campus — and the officers charged with protecting them — remain potential targets for violence.

Evans is the seventh Capitol Police member to die in the line of duty in the department's history, according to the Officer Down Memorial Page, which tracks deaths of law enforcement.

Two officers, one from Capitol Police and another from Washington's Metropolitan Police Department, died by suicide following the January 6 attack.

Almost 140 Capitol Police officers were wounded then, including officers not issued helmets who sustained head injuries and one officer with cracked ribs, according to the officers' union.

It took hours for the National Guard to arrive, a delay that has driven months of finger-pointing between key decision-makers that day.

They were called upon soon afterward to secure the Capitol during Biden's inauguration and faced another potential threat in early March linked to conspiracy theories falsely claiming Trump would retake the presidency.

"Today, once again, these heroes risked their lives to protect our Capitol and our Country, with the same extraordinary selflessness and spirit of service seen on January 6," House Speaker Nancy Pelosi said in a statement.

"On behalf of the entire House, we are profoundly grateful."

The suspect had been taken to the hospital in critical condition.

One of the officers who was injured was taken by police car to the hospital; the other was transported by emergency medical crews.

The US Capitol complex was placed on lockdown after the shooting, and staffers were told they could not enter or exit buildings. Video showed National Guard troops mobilizing near the area of the crash.

Video posted online showed a dark colored sedan crashed against a vehicle barrier and a police K-9 inspecting the vehicle.

Law enforcement and paramedics could be seen caring for at least one unidentified individual.

Biden had just departed the White House for Camp David when the attack occurred.

As customary, he was traveling with a member of the National Security Council Staff who was expected to brief him on the incident.