ROCHESTER, Minn. (AP) – Former U.S. House Speaker Dennis Hastert has arrived at a Minnesota prison to serve his 15-month sentence in a hush-money case involving revelations that he sexually abused at least four boys when he coached wrestling at an Illinois high school.

The 74-year-old Illinois Republican arrived around noon Wednesday at the federal prison in Minnesota where he will be known as Inmate No. 47991-424. Hastert is one of the highest-ranking U.S. politicians to go to prison.

Judge Thomas Durkin branded Hastert “a serial child molester” when he imposed the sentence in April.

Hastert wasn’t charged with child abuse because of statutes of limitation. He coached at Yorkville High School from 1965 to 1981.

Hastert pleaded guilty to violating banking law in trying to pay $3.5 million to keep one victim quiet.