Video report by ITV News US Correspondent Emma Murphy
A man drove a car at two officers manning a barricade around the US Capitol on Friday, the suspect then emerged from the vehicle wielding a knife and lunging at police.
Officer Evans died from his injuries, while a second officer remains in hospital. The suspect in the car was shot dead by police.
President Biden had just departed the White House for Camp David when the incident occurred.
Issuing a statement later on Friday evening, he wrote: "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 and left a fellow officer fighting for his life.
"We send our heartfelt condolences to Officer Evans' family.
"We know what a difficult time this has been for the Capitol, everyone who works there, and those who protect it".
President Biden appears to be referencing the January 6 Capitol riots, which saw a violent mob storm Congress as his election win was being certified.
ITV News US Correspondent Emma Murphy has more:
Police said Friday's incident did not appear to be related to terrorism and said there was no immediate connection to the January 6 riots.
Law enforcement officials identified the suspect as 25-year-old Noah Green.
Investigators were digging into his background and examining whether he had any mental health history as they tried to discern a motive.
They were also working to obtain warrants to access his online accounts.Officers said the suspect did not appear to have been on the police’s radar.
In a statement, Capitol Police Acting Chief Yogananda Pittman said Officer Evans had served with the force for 18 years.
She added: "Please keep Officer Evans and his family in your thoughts and prayers."
Speaking to reporters earlier on Friday, Chief Pittman outlined how the incident had unfolded.
"The suspect rammed his car into two of our officers and then hit the north barricade barrier. At such time the suspect exited the vehicle with a knife in hand," she said.
"Our officers then engaged that suspect. He did not respond to verbal commands. The suspect did start lunging toward US Capitol Police officers. At which time US Capitol Police officers fired upon the suspect.
"It is with a very, very heavy heart that I announce one of our officers has succumbed to his injuries."
Authorities had installed a tall perimeter fence around the Capitol following the riot 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.
Congress was placed under lockdown for a time on Friday afternoon, though lawmakers are currently in recess.
US politicians have also paid tribute to Officer Evans.
Democratic House speaker Nancy Pelosi said: "America’s heart has been broken by the tragic and heroic death of one of our Capitol Police heroes: Officer William Evans. He is a martyr for our democracy."
She continued: "Members of Congress, staff and Capitol workers, and indeed all Americans are united in appreciation for the courage of the U.S. Capitol Police. 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," she added.
"Congress stands ready to assist law enforcement with a swift and comprehensive investigation into this heinous attack.
"May we always remember the heroism of those who have given their lives to defend our Democracy. May it be a comfort to the family of Officer Evans that so many mourn with them and pray for them at this sad time."
Democratic Senate majority leader Chuck Schumer tweeted he was "heartbroken for the officer killed".
"I’m heartbroken for the officer killed today defending our Capitol and for his family. I’m praying for the officer injured and his family."
He added: "We're in their debt"