A vehicle rammed a barricade outside of the United States Capitol Friday, killing a Capitol Police officer and injuring another.

The suspect was shot and killed by authorities after getting out of the car brandishing a knife and started lunging toward the officers, according to Acting U.S. Capitol Police Chief Yogananda Pittman. 

One of the officers succumbed to their injuries, Chief Pittman confirmed at a press briefing following the incident. The officer was later identified as Officer William "Billy" Evans, an 18-year veteran of the force.

“It is with profound sadness that I share the news of the passing of Officer William 'Billy' Evans this afternoon from injuries he sustained following an attack at the North Barricade by a lone assailant," Chief Pittman said in a statement. "Officer Evans had been a member of the United States Capitol Police for 18 years. He began his USCP service on March 7, 2003, and was a member of the Capitol Division’s First Responder’s Unit. Please keep Officer Evans and his family in your thoughts and prayers.” 

Officer Evans is the second member of the Capitol Police to die in the line of duty this year, after Officer Brian Sicknick was killed in the Jan. 6 riot at the U.S. Capitol. Two other officers who responded to the riot — a Capitol Police officer and a D.C. Metropolitan Police Officer — died by suicide.

"This has been an extremely difficult time for U.S. Capitol Police," Chief Pittman said. 

Chief Pittman noted that there is no indication the suspect was targeting any specific member of Congress. Police do not believe that there is an ongoing threat to the area, and the incident is not believed to be terror-related.

The other officer injured is in stable and non-threatening condition, according to the Capitol Police.

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

The suspect had been suffering from delusions, paranoia, and suicidal thoughts, a U.S. official told The Associated Press on Saturday.

In online posts that have since been removed, the suspect described being under government thought control and said he was being watched. He described himself as a follower of the Nation of Islam and its founder, Louis Farrakhan, and spoke of going through a difficult time when he leaned on his faith. Some of the messages were captured by the group SITE, which tracks online activity.

"To be honest these past few years have been tough, and these past few months have been tougher," the suspect wrote in late March. "I have been tried with some of the biggest, unimaginable tests in my life. I am currently now unemployed after I left my job partly due to afflictions, but ultimately, in search of a spiritual journey."

Investigators are increasingly focused on Green’s mental health as they work to identify any motive for the attack, said the official, who was not authorized to speak publicly about an ongoing investigation and spoke to The AP on condition of anonymity. The official said investigators had talked to Green’s family, who spoke of his increasingly delusional thoughts.

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

A spokesperson for the National Guard told Spectrum News that they still had 2,300 guardsmen on duty in Washington, D.C. as of Friday, down from about 25,000 around inauguration day.

The majority of fencing put up for Inauguration Day has also been removed, allowing cars onto nearby streets. But Friday’s incident also happened at a road barrier that was used prior to Jan.6, meant to block daily traffic and admit members of Congress into the Capitol complex.

The National Guard’s spokesperson told Spectrum News that assessing the threat level at the Capitol in recent weeks has been the responsibility of the U.S. Capitol Police in combination with intelligence from the FBI. The National Guard’s role at the Capitol is to support the police force at their request, they said.

Rep. Ro Khanna (D-CA) told CNN he was working in his office at the Cannon Building on Friday but was out picking up lunch when the crash happened. He was waiting in his car afterward for the lockdown to end.

“It's really sad because I had thought once the barriers were removed that we were moving back to some sense of normalcy,” he said. “But this just shows the level of risk that there still is, and really sad that this is happening at the Capitol.”

The incident comes nearly three months after rioters loyal to then-President Donald Trump stormed the Capitol in an attempt to disrupt the certification of Joe Biden's election win. The rioting resulted in five deaths, including Officer Sicknick.

Authorities installed a tall perimeter fence around the Capitol and for months restricted traffic along the roads closest to the building, but they have begun pulling back some of the emergency measures in recent weeks. There was no immediate connection apparent between Jan. 6 and Friday’s crash.

The House and Senate are in recess, and lawmakers are not at the Capitol.

President Joe Biden issued a statement from Camp David, saying that he and First Lady Dr. Jill Biden are "heartbroken" by the attack that took Officer Evans' life and left another officer "fighting for his life."

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

The president ordered the flags at the White House to be flown half-staff in a presidential proclamation honoring "the service and sacrifice of the victims of the attack at the United States Capitol on Friday, April 2."

Biden also expressed "the nation’s gratitude to the Capitol Police, the National Guard Immediate Response Force, and others who quickly responded to this attack."

Homeland Security Secretary Alejandro Mayorkas said that "there is still much to be determined about this attack" and expressed his condolences for Officer Evans and his loved ones.

"My thoughts and prayers go out to the family, friends, & colleagues of the Capitol Police Officer who lost his life today protecting the symbol of our democracy," Mayorkas said.

Other White House officials, including Transportation Secretary Pete Buttigieg, also expressed sympathies for Officer Evans.

"Our hearts break for the U.S. Capitol Police officer who was killed, and we are holding in our prayers the officer injured at the U.S. Capitol," Buttigieg wrote on Twitter. "I am deeply grateful for the service of the men and women who keep our government and public servants safe."

Attorney General Merrick Garland has been briefed on the incident and is actively monitoring the situation, according to a spokesperson. 

Lawmakers on both sides of the aisle expressed their prayers for the Capitol Police officers injured.

House Speaker Nancy Pelosi ordered the flags at the Capitol to be flown at half-staff in honor of Officer Evans, according to a spokesman.

In a statement, Pelosi called Officer Evans "a martyr for our democracy."

"Members of Congress, staff and Capitol workers, and indeed all Americans are united in appreciation for the courage of the U.S. Capitol Police," Pelosi said. "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.  On behalf of the entire House, we are profoundly grateful."

Senate Majority Leader Chuck Schumer said he is "heartbroken" for Officer Evans and for his family, adding: "We're in their debt."

"We thank the Capitol Police, National Guard, & first responders for all they do to protect the Capitol and those inside," Schumer added.

Sen. Marco Rubio (R-FL) wrote on Twitter that "we are all horrified by this tragic & cowardly attack on U.S. Capitol police officers."

"We are heartbroken for their families, loved ones & the entire force," he continued. "May God bless them in this time of unbearable grief & protect them in the days ahead."

"My heart is heavy," Sen. Amy Klobuchar (D-MN) wrote on Twitter. 

"One of our US Capitol Police officers has passed away protecting our democracy," she said. "I’m keeping their family, loved ones, and the entire Capitol Police force in my prayers."

"Please join me in prayer for the two Capitol Police officers and their families," House Minority Leader Kevin McCarthy (R-CA) wrote on Twitter. "They reacted quickly and bravely, as did all the other first responders at the scene. The whole country is pulling for them right now."

"Deeply saddened to learn a U.S. Capitol police officer has died today from another violent attack on our nation’s capital," Sen. Sherrod Brown (D-OH) wrote on Twitter.

"Our hearts and prayers are with the officer’s family and friends, as well as the other officer injured in the attack," Brown added.

"I am heartbroken that Officer Evans was killed today in the line of duty," Senate Minority Leader Mitch McConnell (R-KY) wrote. "On this Good Friday, let's all pray for healing for the surviving officer, comfort for Officer Evans’s family, and for all the officers and families of the United States Capitol Police."

“I am heartbroken to learn that one of the U.S. Capitol Police officers involved in today’s incident has been killed in the line of duty," House Majority Leader Steny Hoyer (D-MD) said in a statement. "The officer’s family will be in my thoughts, and I pray for the health and well-being of the other officer injured. They and their fellow officers displayed great courage and professionalism in protecting the Capitol and those inside, quickly taking control of the situation and neutralizing the threats.

The Associated Press contributed to this report.