The indictment of former House speaker J. Dennis Hastert was triggered by an effort he made to hide payments of hush money to a male student he allegedly sexually molested decades ago, a federal law enforcement official said Friday.

The indictment asserts that the acts Hastert wanted to conceal date to a time when he was a teacher and coach in Illinois before entering politics in the early 1980s, the official said. Authorities said the alleged victim, who has spoken with law enforcement officials, was one of Hastert’s students.

Hastert, the longest-serving Republican speaker in House history, is not expected to face molestation charges because authorities don’t think they have enough evidence to bring a case against him, a law enforcement official said.

A federal grand jury in Chicago indicted the former speaker, 73, Thursday on charges that he violated banking laws in a bid to pay $3.5 million to an unnamed person to cover up “past misconduct.” The alleged victim is that person, the official said.

The case has riveted and shocked Washington, where Has­tert has been a high-paid lobbyist since his 2007 retirement from Congress.

Hastert announces that he will not seek reelection for a 12th term as he stands on the steps of the Kendall County courthouse with, from left, his son Josh; wife, Jean; daughter-in-law Heidi and grandson Jack, in Yorkville, Ill., on Aug. 17, 2007. (Brian Kersey/AP)

“The Denny I served with worked hard on behalf of his constituents and the country. I’m shocked and saddened to learn of these reports,” House Speaker John A. Boehner (R-Ohio) said in a statement released Friday.

Law enforcement officials said that at first they didn’t know what to make of a series of large cash withdrawals Hastert began making in 2010.

It was only after FBI agents interviewed Hastert in December, officials said, that investigators began piecing together the details. In that interview, the indictment said, Hastert lied to the agents, telling them he made the withdrawals because he didn’t feel safe keeping his money in the banking system.

“Yeah . . . I kept the cash. That’s what I’m doing,’’ Hastert was quoted as telling agents.

Actually, court documents said, Hastert was scheming to mask more than $950,000 in withdrawals from various ac­counts, in violation of federal banking laws that require the disclosure of large cash transactions.

Hastert has not spoken publicly about the case, and efforts to reach him have been unsuccessful. One of his sons, a Chicago lawyer, has not responded to requests for comment. No lawyer or representative has spoken out on Hastert’s behalf, either.

If convicted of seeking to evade banking laws and lying to the FBI, the former House speaker could face up to 10 years in prison, prosecutors said.

The Post's Chris Cillizza breaks down former House speaker Dennis Hastert's indictment on charges that he broke bank laws by withdrawing large sums of money and lying about it to federal authorities. (Nicki DeMarco/The Washington Post)

From Washington to Yorkville, former Hastert associates were left stunned at the turn of events, calling and e-mailing one another to express confusion. They said they did not know where their former boss was holed up during the biggest crisis of his career.

“Anyone who knows Denny is shocked and confused” by the indictment, Sen. Mark Kirk (R-Ill.) said Friday. He said Hastert should have “his day in court to address these very serious accusations,” and he called the case “a very troubling development.”

Don Davidson, who taught history with Hastert at Yorkville High School between 1970 and 1977, said he was “astounded.” He added that Hastert “was a good teacher, and he treated the students fairly.’’

Davidson, who also coached the basketball team at Yorkville, said he “never heard anything along those lines” about allegations of misconduct on the part of the former speaker.

The allegations have landed with near-universal disbelief in the small communities along the Fox River in northeastern Illinois where Hastert grew up, worked and lived for decades. While tract houses and strip malls continue to claim farmland here, about 50 miles west of Chicago, it’s still a place where a slow-moving combine can slow a commute.

On Friday, the release of students from Yorkville High School was made even more hectic by the presence of news trucks and TV cameras. Across the street, in a small upstairs room in the Yorkville Public Library, reporters pored over old yearbooks, seeking photos of Hastert and his champion wrestling teams.

In a statement Friday, the Yorkville school district that employed Hastert from 1965 to 1981 said it first learned about the charges when Hastert was indicted.

“Yorkville Community Unit School District #115 has no knowledge of Mr. Hastert’s alleged misconduct, nor has any individual contacted the District to report any such misconduct,” the statement said. “If requested to do so, the District plans to cooperate fully with the U.S. Attorney’s investigation into this matter.”

Bob Evans, 70, who taught alongside Hastert for 14 years at Yorkville High, serving as his assistant wrestling coach for some of them, said he never heard even a whisper about any wrongdoing on Hastert’s part.

“I can’t believe it,” he said, standing in his driveway, on a street where Hastert once lived. “The people I’ve talked to in Yorkville that know him, they’re just absolutely shocked.”

Evans recalled Hastert as being devoted to wrestling to the point that he would travel across the country to learn a new wrestling move to give his wrestlers an advantage in Illinois.

“He mentored a lot of kids. He was an integral part of their lives,” he said. “He was never a screamer. He was a demander. He wanted the best from them.”

As a coach, Evans said, Hastert had a knack for getting the most out of wrestlers with average athletic talent through hard work. Hastert’s coaching career culminated in a 1976 state championship.

“It throws a black cloud over what he did all those years,” he said. “They won conference championships, state championships. They were good people. They were good kids.”

“If it did happen,” Evans added, “then get it out . . . but you just got to hope it isn’t as bad as it seems.”

Dan McNeive was a social studies teacher and basketball coach at Yorkville High from 1978 to 1981. His classroom adjoined Hastert’s. “I came there from a much larger high school, so it was kind of culture shock for me. But Denny was certainly a good colleague and he kind of taught me the ways of the small town,” said McNeive, who is now retired and living in Arizona. “We were pretty close the three years I was there.”

McNeive said many of the teachers at Yorkville were friends and did things together socially. “It was a pretty tight group,” he said. He said he had received many phone calls from former Yorkville colleagues since news broke about the allegations against Hastert. “Everyone pretty much says the same thing — it’s just hard to believe and no clue at all,” McNeive said. “It definitely came as a total shock to us.”

Hastert became House speaker almost by accident but wound up serving in the post for nearly a decade. Rep. Newt Gingrich (R-Ga.), far more flamboyant than the low-key Hastert, stepped down as speaker following the disappointing Republican performance in the 1998 midterm elections.

After revelations that Gingrich’s would-be replacement, Rep. Bob Livingston (R-La.), had engaged in extramarital affairs, Hastert emerged as a unity candidate.

Some conservative activists, who had clashed with Hastert in the past, on Friday recalled him as a figure known for his avuncular personality but rarely — if ever — embraced by the GOP’s base.

“I called for his resignation during the Mark Foley scandal for mishandling it,” said David Bossie, a former House GOP staffer, referring to the 2006 resignation of Rep. Mark Foley (R-Fla.) in the wake of allegations that he had for years sent explicit messages to male congressional pages.

“If he had lifted his finger to find one shred of evidence, he would have found evidence of what Foley was up to,’’ said Bossie, who is now president of Citizens United, a conservative advocacy group.

Democrats mostly resisted criticizing Hastert. Former Republican National Committee chairman Haley Barbour warned Democrats not to make the controversy a political cudgel.

“It doesn’t matter a bit politically,” Barbour said in a telephone interview from Mississippi, where he previously served as governor. “Democrats hope it does, but I don’t think so.”

The indictment did not spell out the nature of what it described as “prior misconduct” by Hastert, but it noted that before entering state and federal politics in 1981, Has­tert served for more than a decade as a teacher and wrestling coach in Yorkville.

In 2010, confronted about the “prior misconduct,” the former speaker agreed to pay $3.5 million to the person “to compensate for and conceal his prior misconduct against Individual A,” prosecutors alleged.

A review of Hastert’s real estate holdings and other investments, as well as his lobbying career, shows he may have been equipped to handle such a payment. He made a small fortune in real estate before leaving Congress then embarked on a lucrative lobbying career after leaving. Among his clients: Peabody Energy, the Secure ID Coalition, Lorillard Tobacco and Fuels America.

The person who Hastert agreed to pay had known Hastert most of his life, growing up in Yorkville, the city next to Hastert’s home town of Plano, in the exurbs west of Chicago, the indictment said. Prosecutors said the actions “occurred years earlier” than the 2010 meeting that sparked the payments.

Over five years, Hastert withdrew about $1.7 million in cash from his various bank accounts — at one point in 2014 delivering $100,000 a month to the person in question, the indictment alleged.

The case has been assigned to U.S. District Judge Thomas M. Durkin, who will set dates for Hastert’s arraignment and other court proceedings, Kim Nerheim, a spokeswoman for the U.S. attorney’s office for the Northern District of Illinois, said Friday. At the arraignment, Hastert will be asked to enter a plea.

Durkin, 61, is a former federal prosecutor nominated to the federal bench by President Obama in 2012. He is the older brother of Jim Durkin, a Republican member of the Illinois House of Representatives, where Hastert served in the 1980s.

Horwitz and Markon reported from Washington. Robert Costa, Paul Kane, Alice Crites, Scott Higham, Robert O’Harrow Jr., William Branigin and Emma Brown in Washington contributed to this report.