He was a member of the first responders unit and an 18-year veteran of the U.S. Capitol Police.
One person has died after slamming a vehicle into the security barrier surrounding the Capitol building, United States media report.
Pittman says the suspect rammed a barricade near the US Capitol.
"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.
However, White House press secretary said she is not aware of the situation at Capitol yet.
Five people died in the January 6 riot, including Capitol Police officer Brian Sicknick, who was among a badly outnumbered force trying to fight off insurrectionists who supported former president Donald Trump's bid to overturn the election.
The House and Senate are now on recess, but some lawmakers, staff, and reporters were working on Capitol Hill.
"It is with a very, very heavy heart that I announce one of our officers has succumbed to his injuries".
The death is the latest moment of sorrow for a department after the loss of Brian Sicknick, who clashed with rioters during the January 6 insurrection and died a day later, and Howard Liebengood, who committed suicide weeks after that.
"This has been an extremely hard time for the US Capitol police after the events of 6 January, and after the events that have occurred here today", she said.
Police block a street after a vehicle drove into police officers near the US Capitol building in Washington, US, April 2, 2021.
The suspect was shot and died at a hospital, officials said. Law enforcement sources tell ABC News the suspect is dead.
But, Ms Pittman said, they also remain on edge.
The security checkpoint is typically used by senators and staff on weekdays, but senators are away for recess.
Speaker Nancy Pelosi has ordered the Capitol flags to be flown at half mast in honour of the officer killed in the attack.
In recent weeks some security around the complex has been loosened, with the number of armed National Guard troops at the Capitol reduced and a security fence that created a broad perimeter around the Capitol complex removed. As customary, he was traveling with a member of the National Security Council Staff who was expected to brief him on the incident.