Security around the U.S. Capitol remained tight on Saturday, a day after a man rammed a car into two officers at a barricade outside.
One of the officers was killed before police shot the suspect, 25-year-old Noah Green, who died at a hospital.
Green had been suffering from delusions, paranoia and suicidal thoughts, a U.S. official told The Associated Press on Saturday.
Investigators believe it was an isolated incident from a disturbed young man.
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 officer's death was the second line-of-duty death this year for the U.S. Capitol Police, still struggling to heal from the Jan. 6 insurrection.
Authorities installed a giant fence around the Capitol perimeter and for months restricted traffic along the roads closest to the building, but they had begun pulling back some of the emergency measures.
The most recent incident could delay the gradual reopening of the buildingâ€™s grounds to the public.