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The ringleader behind a $25 million college admission scam that implicated dozens of people, including Hollywood actresses Lori Loughlin and Felicity Huffman, said he has worked with more than 750 families.

William Rick Singer, who pleaded guilty Tuesday in a Boston federal court to racketeering, money laundering, conspiracy and obstruction of justice charges, said in a phone conversation recorded by the FBI that he helps "the wealthiest families in the U.S. get their kids into school."

Singer said he facilitated 761 "side doors" to admission.

"They want guarantees, they want this thing done. They don't want me messing around with this thing," he said, according to court documents unsealed Tuesday. "And so they want in at certain schools."

According to the investigators, parents paid Singer millions to boost their kids' chances of getting into schools such as Yale University, Stanford University and Georgetown University by paying people to take tests for their children, bribing test administrators to allow that to happen, and bribing college coaches to identify the applicants as athletes.

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Singer, 58, faces a maximum sentence of 65 years if convicted.

"I am absolutely responsible for it," he told U.S. District Judge Rya W. Zobel. "I put everything in place. I put all the people in place and made the payments directly."

Some of the parents spent between $200,000 to $6.5 million to ensure their children would get into the schools. Singer said the price depended on what school the parents wanted their kids to get into, according to the court documents unsealed Tuesday.

Loughlin and Huffman were among 50 people charged in the alleged scam Tuesday. Loughlin and her husband, Mossimo Giannulli, agreed to pay $500,000 to help their two daughters' chances of gaining admission to the University of Southern California, court papers say.

Loughlin allegedly said that she would arrange for her daughter to be photographed so it appeared she was the crew coxswain on the L.A. Marine club’s rowing team, according to a criminal complaint.

Huffman and her husband, actor William H. Macy, paid $15,000 to get their daughter unlimited time for her SAT test, prosecutors say.

Huffman also allegedly discussed the idea of having a ringer take the test for their other daughter but ultimately decided against it after she expressed concern about having to explain the difference in scores to her daughter’s tutor, according to the complaint.

"I just didn't know if it'd be odd for [the tutor] if we go, "Oh, she did this in — in March 9, but she did so much better in May," Huffman allegedly said on the call. "I don't know if that’d be like — if [the tutor] would be like, 'Wow.'"

In other instances, Singer is accused of paying people to create fake athletic profiles for his clients’ sons and daughters and then bribing college coaches to give those students slots meant for incoming athletes.