Cole Tomas Allen is the California man accused of shooting during the White House Correspondents' Dinner on Saturday.
At a press conference Monday afternoon, acting U.S. Attorney General Todd Blanche said Allen traveled by train to Washington, D.C.
"The Department of Justice approaches incidents like this with urgency and clarity of purpose," Blanche said.
The 31-year-old of Torrance, California is a highly educated tutor and amateur video game developer. In a message sent to family members just minutes before the attack, including to his brother in Connecticut, Allen described himself as a "Friendly Federal Assassin."
"How he got to that position is not clear, but it's clear that somehow he radicalized and got to that point of view, and when he does that, he joins a long list of narcissists who have felt necessary to take action on their own," said Ken Gray, retired FBI special agent.
Gray read Allen's alleged manifesto and posts he made on the social media app BlueSky.
There's no indication that Allen had ever previously been charged with a crime. He faces several charges including attempted assassination of a president.