According to CNN, US President Joe Biden reacted to the incident saying he and first lady Jill Biden are heartbroken.
"Jill and I were heartbroken to learn of the violent attack at a security checkpoint on the US Capitol grounds, which killed Officer William Evans of the US Capitol Police, and left a fellow officer fighting for his life," Biden said.
"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.
"I have been receiving ongoing briefings from my Homeland Security Advisor, and will be getting further updates as the investigation proceeds," he added.
Biden also said he has ordered that the White House flags be lowered to half-mast.
United States House Speaker Nancy Pelosi has ordered the flags at the US Capitol to be flown at half-staff to commemorate the death of the US Capitol Police (USCP) officer.
Taking to Twitter Pelosi's Deputy Chief-of-Staff, Drew Hammill said: "Speaker Pelosi has ordered the flags at the US Capitol to be flown at half-staff due to the death of a US. Capitol Police Officer in line of duty today. The process of lowering the flags may take longer than usual because of the Capitol's current lockdown status."
At a press conference earlier on Friday, USCP Acting Chief Yogananda D. Pittman said: "I just ask that the public continue to keep US Capitol Police and their families in your prayers," she said.
Pittman said that US Capitol Police shot and killed a man who rammed a car into a security barrier outside the Capitol building on Friday, injuring one officer and killing another.
The Capitol was on security lockdown, with no one allowed to enter or exit buildings, but they are allowed to move within the campus of buildings.
"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," Pittman said. Evans, had been a member of the USCP for 18 years and was a member of the Capitol Division's First Responder's Unit.
Multiple news media reports have also identified the man who rammed a blue sedan vehicle into the North Barricade at the Capitol striking two officers and then exiting to charge at them with a knife has been identified.
CNN quoted sources from the Federal and local law enforcement stating that suspect has been identified as Noah Green. The news outlet quoted one federal source stating that Green was 25 years old from Indiana.
Later the police said that lockdown was lifted and the USCP has "cleared the external security threat incident located at all of the Capitol Campus buildings, however the area around the crime scene will continue to be restricted and individuals should continue to follow police direction."
In a tweet, the police department said the condition of the second officer was stable and non-threatening.
Acting Metropolitan Police Chief Robert Contee said the investigation into the incident was ongoing. Investigators do not yet have a motive for the attack, but do not believe the incident was "terrorism related" at this time, Chief Robert Contee of the Washington Metropolitan Police Department told reporters.
"It does not appear to be terrorism-related. But obviously, we'll continue to investigate to see if there is some type of nexus along those lines," he said at a news conference Friday.
According to videos shared on social media a a helicopter was spotted landing in the area to respond to the incident. National Guard troops were also seen lining up with their shields at various intersections near the Capitol.
The officer who was killed today is the second to die in the line of duty this year. Capitol Police officer, Brian D. Sicknick, died a day after the Capitol riots on January 6 "due to injuries sustained while on duty," the Capitol Police said in a statement. Two officers died by suicide after responding to the riot.