Multiple media organizations, citing anonymous sources, named the suspect as Noah Green, 25, of Newport News, Virginia. Green's brother told the Washington Post that his sibling struggled with drug use and paranoia and his family worried about his mental state.
According to media reports, Green spoke on Facebook about the "end times", the anti-Christ, and government "mind control". He also said he was unemployed after leaving his job, "partly due to afflictions," and praised Nation of Islam leader Louis Farrakhan.
Facebook said in a statement that it removed the suspect’s accounts from Facebook and Instagram and were in contact with law enforcement.
Brendan Green told the Washington Post his brother had been violently ill on Thursday evening at the Virginia apartment they shared, and later sent him a text message saying that he planned to become homeless.
Police said the suspect was not known to them, and they had yet to determine what motivated him.
"Clearly this was someone who was actively trying to just get at whoever or whatever - we just don't know right now," Contee said. "Whether the attack was at law enforcement, or whoever, we have a responsibility to get to the bottom of it and we'll do that."
Dozens of police cars, marked and unmarked, raced toward the iconic domed white building, in an unwelcome reminder of Jan. 6, when thousands of supporters of then-President Donald Trump overran the complex.
It was the worst security threat at the Capitol since that day, when scores of Capitol police were wounded, one was killed and two others later committed suicide.
U.S. spy agencies warned in mid-March of an ongoing threat that racially motivated violent extremists, such as white supremacists, will carry out mass-casualty attacks on civilians while militia groups target police and government personnel and buildings.
Roads leading to the complex were blocked by police cars or officers and people inside the Capitol were told to stay away from windows for much of the afternoon before police announced that the lockdown had been lifted.
Videos and photographs from the scene showed a blue car rammed into a security barricade, a front door open.