The authorities have said that the suspect in the Saturday attack was taken into custody shortly after charging through a security checkpoint and exchanging gunfire with federal law enforcement officials inside the Washington Hilton. He was armed with knives, a shotgun, and a handgun, authorities have said.

The suspect is initially expected to be charged with two counts of using a firearm and one count of assault on a federal officer using a dangerous weapon, Jeanine Pirro, the U.S. attorney for the District of Columbia, said on Saturday. He is scheduled to be arraigned on Monday in Federal District Court and additional charges are expected, she said.

Mr. Allen was born the oldest of four siblings in Los Angeles County.

As of Saturday night, Mr. Allen’s father was listed online as an elder at Grace Torrance, which describes itself as a Protestant church in the Reformed tradition.

In 2013, Mr. Allen enrolled at the California Institute of Technology, or Caltech, an elite research university in Pasadena, Calif. At that time, according to federal data, Caltech admitted less than 11 percent of its undergraduate applicants.

There, Mr. Allen studied mechanical engineering. He graduated with a 3.0 GPA, according to his LinkedIn profile.

In the summer of 2014, he did a summer internship at NASA’s Jet Propulsion Laboratory, according to his LinkedIn profile. And a local news clip from 2017 shows Mr. Allen, clad in a checkered collared shirt and sweater, demonstrating his design for a wheelchair emergency brake at a conference focused on designing products for older people.

He was also involved in the Nerf Club, in which members armed with foam toys organized campus battles, and belonged to a campus Christian fellowship. Another fellowship member recalled that while Mr. Allen was generally quiet and studious, he was not shy about defending his own interpretation of his faith.

“He was definitely a strong believer in evangelical Christianity at the time that I knew him,” the fellowship member, Elizabeth Terlinden, said.

After graduating from Caltech in 2017, Mr. Allen spent several years working as a mechanical engineer, a self-employed video game developer and a college test-prep tutor, according to his LinkedIn profile.

In 2022, he enrolled at California State University, Dominguez Hills, to pursue a master’s degree in computer science. The university said in a statement on Saturday that it had a record of a student matching Mr. Allen’s name earning a degree in 2025.

Bin Tang, a professor of computer science at the university, taught Mr. Allen in several classes.

“I am very shocked to see the news,” Dr. Tang said in an email. “He was a very good student indeed, always sitting in the first row of my class, paying attention, and frequently emailing me with coursework questions.”

Records shared by the two law enforcement officials show that Mr. Allen bought a handgun in October 2023 and a shotgun in August 2025.

According to the note shared by authorities, Mr. Allen told his colleagues and students in recent days that a personal emergency would keep him from his tutoring duties and told his parents that he had “an interview.”

Then he took a train from Los Angeles to Washington via Chicago, checking into the Hilton hotel a day or two before the hotel hosted the White House Correspondents Association dinner, Todd Blanche, the acting attorney general, told “Meet the Press” on Sunday.

Mr. Blanche added that initial evidence indicated that Mr. Allen had acted alone.

Alan Blinder, Devlin Barrett, Sonia A. Rao, Pooja Salhotra, Orlando Mayorquín, Laurel Rosenhall, Jin Yu Young, and Stephanie Saul contributed reporting. Georgia Gee contributed research.