WASHINGTON — Soon after President Donald J. Trump’s inauguration in January 2017, the White House told State Department officials that they needed to find a job for a political appointee.
Federico G. Klein had been a low-level aide on Mr. Trump’s 2016 campaign and a stalwart supporter of the president, outspoken on his religious and conservative views. When a senior State Department official tried to object, believing Mr. Klein to be out of his depth in the world of diplomacy, he was overruled, according to a former department official. Mr. Klein was stashed in obscure positions with little influence.
Four years later, Mr. Klein, 42, finally made his mark in Washington — as a leader of the mob that stormed the Capitol on Jan. 6, according to a court document filed by the F.B.I., which arrested Mr. Klein on Thursday. He is the first known participant in the Capitol breach to have worked for Mr. Trump’s campaign or held a political appointment in his administration.
Interviews with several people who know or worked with Mr. Klein suggest a man with increasingly fiery social and political views, but a forgettable professional record in government and the military. He had offered few public hints that he would be capable of violent political action.
Mr. Klein is visible in video footage from the Capitol wearing a collared shirt and a crew neck sweater under a drab green coat, with a red “Make America Great Again” hat. According to the F.B.I. complaint, he used a stolen Capitol Police riot shield to assault officers and wedge open a door they were trying to shut against the pressing crowd.
“We need fresh people, need fresh people,” Mr. Klein called back to his compatriots from the front of the line charging the police defenses, according to the F.B.I. complaint.
He was arrested after the F.B.I. received a tip from two people who recognized his square-jawed, sandy-haired image from a poster seeking information about Capitol rioters captured on camera.
On paper, he hardly seemed a revolutionary.
Mr. Klein, who goes by Freddie, grew up in an affluent suburb of Washington, D.C., attended George Mason University, joined the Marine Corps as a reservist and volunteered for mainstream Republicans, including Mitt Romney in his 2012 presidential campaign, before signing on with Mr. Trump.
He left little mark in the workplace. Several State Department officials and Trump political hands said that they had no memory of Mr. Klein, and that his role on the 2016 campaign — for which he reported just $15,000 in income in a financial disclosure form — would have been marginal.
He served in the Marine Corps Reserves from early 2004 to late 2012 as a combat engineer, reaching the rank of corporal, according to records released by the Defense Department. Those records also indicate service that was unremarkable.
He did serve a tour of duty in Iraq, in 2005, according to his mother, Cecilia Klein. She said he never fired his weapon there.
At an initial hearing on Friday, Zia M. Faruqui, a magistrate judge in Washington, ordered Mr. Klein held until his bail hearing on Tuesday. Mr. Klein did not respond to a request for comment, and his lawyer, Michelle M. Peterson, a federal public defender, declined to comment on his case.
One person who has known him for many years said Mr. Klein was a loner who could be socially awkward. His mother said nothing in his past would have suggested him capable of joining a violent riot.
“Normal schools, decent grades, went to college,” she recalled during an interview on Friday. “It was all perfectly suburban.”
According to the F.B.I., Mr. Klein held a top-secret security clearance that was renewed in 2019. Such clearances are not unusual for military service members, and his LinkedIn page says his was granted by the Defense Department. It is not clear what responsibilities he carried that would have earned the clearance. The person who has known him for years said he seemed to conjure an air of secrecy about his military service.
Under pressure from the White House in early 2017, Mr. Klein, whose father was from Argentina and had worked at the Inter-American Development Bank before his death, was installed in the State Department’s Office of Brazilian and Southern Cone Affairs as a special assistant. After Secretary of State Rex W. Tillerson expanded an office that handles Freedom of Information Act requests, viewed by many in government as an unrewarding outpost, Mr. Klein’s superiors transferred him there.
People who encountered him at work said he advertised his opposition to abortion rights and support for Mr. Trump’s plans to build a wall along America’s southern border with Mexico.
His social media network and postings suggest a man with deep religious and conservative beliefs and a loathing for Democrats including Hillary Clinton. In 2016, he posted a photo on Facebook of himself posing next to a cardboard cutout of Mrs. Clinton and pretending to grab her by the hair. In an accompanying comment, he said he was “mocking her ugliness.”
Many of his other Facebook postings feature religious art and iconography, as well as images of Mr. Trump. In October, he posted a video of anti-abortion protesters being removed by the police from the waiting room of a family planning clinic as they shouted, “Mommy, stop the murder!” He also posted messages complaining about N.F.L. players refusing to stand for the national anthem, and other messages supporting gun rights and opposing gay rights.
His LinkedIn page features an endorsement of his skills from Eugene Delgaudio, a prominent Washington-area conservative activist known for his outspoken opposition to gay rights, including a 2010 claim that Transportation Security Administration pat-downs were part of a “homosexual agenda.” Mr. Klein’s mother said her son had worked briefly for Mr. Delgaudio, who did not respond to a request for comment.
Mr. Klein’s account with Goodreads, a site for book lovers, lists him as having read several books about military affairs, including the memoir of a German World War II soldier and a biography of Erwin Rommel, a Nazi general. Also listed are several books about dystopian government and society, including “Fahrenheit 451,” “Animal Farm” and “1984,” as well as a history of America’s revolutionary founders.
Mr. Klein graduated from George Mason University in 2002, where he studied political science. Politico earlier reported his arrest.
He told the judge on Friday that after his arrest he had been detained in unsanitary conditions, where cockroaches crawled over him as he slept. Judge Faruqui told him that the D.C. jail where he would be held would be nicer.
In an interview, his mother, who worked in the Office of the United States Trade Representative before her retirement, expressed confusion and dismay at her son’s plight, saying that he had told her that he was “on the Mall” on Jan. 6 but “did not go in the building.”
She said news organizations were unfairly singling out her son because of his affiliation with Mr. Trump.
“You know why they’re putting so much pressure on this. It’s because of the T-word. If he hadn’t done a stint for the campaign, no one would complain,” she said. “This is the only one I’m aware of — besides the guy with the horns and the spear — who is getting the kind of treatment that Fred’s getting.”
She added that she was confident others like him participated in the riot.
“If you don’t think there were a few other political appointees out in those crowds, I think you’re being very naïve,” she said.
Reporting was contributed by Susan C. Beachy, Katie Benner, Helene Cooper and Lara Jakes.