Authorities investigate the scene after a man rammed a car into two officers at the barricade on Capitol Hill in Washington, April 2, 2021. (ALEX BRANDON / AP)

WASHINGTON -A motorist rammed a car into US Capitol police on Friday and brandished a knife, killing one officer and injuring another and forcing the Capitol complex to lock down in an attack that police said did not appear to be terrorism-related.

Police shot and killed the suspect.

Yogananda Pittman, acting chief of the US Capitol Police, said the suspect drove into the officers, then hit a barricade and got out of the vehicle, lunging at them with a knife.

President Joe Biden said he was heartbroken by the attack and ordered flags at the White House be lowered to half-staff

“It is with a very, very heavy heart that I announce one of our officers has succumbed to his injuries,” she told a news conference, her voice choked with emotion.

Police identified the slain officer as William “Billy” Evans, an 18-year veteran of the force and father of two children. Officials said the other officer was in a stable and non-life threatening condition.

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“It does not appear to be terrorism-related but obviously we’ll continue to investigate,” said Robert Contee, acting chief of the Metropolitan Police Department of Washington.

President Joe Biden said he was heartbroken by the attack and ordered flags at the White House be lowered to half-staff. In a statement, he said he was being briefed on the investigation.

Multiple media organizations, citing anonymous sources, named the suspect as Noah Green, 25, of Newport News, Virginia. Green’s brother told the Washington Post that his sibling struggled with drug use and paranoia and his family worried about his mental state.

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According to media reports, Green spoke on Facebook about the “end times”, the anti-Christ, and government “mind control”. He also said he was unemployed after leaving his job, “partly due to afflictions,” and praised Nation of Islam leader Louis Farrakhan.

Facebook said in a statement that it removed the suspect’s accounts from Facebook and Instagram and were in contact with law enforcement.

Brendan Green told the Washington Post his brother had been violently ill on Thursday evening at the Virginia apartment they shared, and later sent him a text message saying that he planned to become homeless.

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Police said the suspect was not known to them, and they had yet to determine what motivated him.

Dozens of police cars, marked and unmarked, raced toward the iconic domed white building, in an unwelcome reminder of Jan 6, when thousands of supporters of then-president Donald Trump overran the complex.

It was the worst security threat at the Capitol since that day, when scores of Capitol police were wounded, one was killed and two others later committed suicide.

US spy agencies warned in mid-March of an ongoing threat that racially motivated violent extremists, such as white supremacists, will carry out mass-casualty attacks on civilians while militia groups target police and government personnel and buildings.

Roads leading to the complex were blocked by police cars or officers and people inside the Capitol were told to stay away from windows for much of the afternoon before police announced that the lockdown had been lifted.