A U.S. Capitol Police officer was killed, and a second officer was injured, when they were rammed by a vehicle at the U.S. Capitol security perimeter on Friday afternoon, authorities said.

NPR has confirmed the identity of the suspect as 25-year-old Noah Green. Various media reports have identified Green as well. He exited his car a with a knife and lunged at officers, according to Acting Capitol Police Chief Yogananda Pittman, and officers opened fire and killed him.

Both officers were taken to a hospital, at least one by helicopter. The deceased officer was identified as William “Billy” Evans, an 18-year veteran of the force. He was a member of the First Responder’s Unit, according to USCP.

The second officer who was struck by the car is in stable and non-life threatening condition, police said.

U.S. Capitol Police described the suspect as a “lone assailant.”

The attack took place at the North Barricade access point along Constitution Avenue around 1 p.m., and the U.S. Capitol complex was placed under lockdown for several hours.

President Joe Biden issued a statement saying he was “heartbroken,” and ordered flags at the White House to half-staff.

“We send our heartfelt condolences to Officer Evans’ family, and everyone grieving his loss. We know what a difficult time this has been for the Capitol, everyone who works there, and those who protect it,” the president said in the statement.

This attack comes less than three months after the Jan. 6 insurrection at the Capitol prompted a review of security measures around the building.

“I just ask that the public continue to keep U.S. Capitol Police and their families in your prayers,” Pittman said at a press conference. “This has been an extremely difficult time for U.S. Capitol Police.”

In the wake of the security failures on Jan. 6, police erected seven-foot black metal fences topped with razor wire around the Capitol grounds’ perimeter, blocking off much of the area from traffic. Members of the public and advocacy groups criticized the idea of permanent fencing — a petition in opposition has collected nearly 34,000 signatures.

Police had recently reduced the fencing around the Capitol from 3 miles to 1.25 miles, reopening some surrounding roads. Security officials said they were prepared to “ramp up security at a moment’s notice if needed.”

The AP noted that the incident occurred at an existing security checkpoint used by Congress members and staffers when in session (it is currently on recess). Video from eyewitnesses shows a blue sedan rammed into the barricade with the driver’s side door open. National Guard troops, which remain on duty in D.C. following the insurrection, also responded to the scene.

Charles Allen, who represents Ward 6, which includes the Capitol Hill neighborhood, on the D.C. Council, mourned the officer’s death on Twitter.

“We know very little yet about today’s incident at the U.S. Capitol,” he said. “But we do know at least one officer who showed up to work today will not be coming home to their loved ones.”

The D.C. Metropolitan Police Department will take over the investigation, Acting Police Chief Robert Contee said at the press conference.

Police officers closed Constitution Avenue between Second Street NE and First Street NW, as well as First Street between Constitution Avenue NE and Independence Avenue SE.

This story has been updated to include more recent information about the suspect. Colleen Grablick, Jordan Pascale, Debbie Truong and Ally Schweitzer contributed reporting.