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Hollywood actresses Lori Loughlin and Felicity Huffman are among 50 people charged in a $25 million college entrance exam cheating scheme, according to court documents unsealed in Boston on Tuesday.

The alleged scam focused on getting students admitted to elite universities as recruited athletes, regardless of their athletic abilities, and helping potential students cheat on their college exams, according to the indictment.

Felicity Huffman and Lori Loughlin AP; NBC

Authorities said the FBI investigation, code-named Operation Varsity Blues, uncovered a network of wealthy parents who paid thousands of dollars to a California man who boosted their children's chances of gaining entrance into elite colleges, such as Yale and Stanford, 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.

"This case is about the widening corruption of elite college admissions through the steady application of wealth, combined with fraud," U.S. Attorney for Massachusetts Andrew Lelling said.

"There can be no separate college admission for the wealthy, and I will add there will not be a separate criminal justice system either," he said.

Lelling stressed that the colleges themselves are not targets of the investigation, which is ongoing. No students were charged, and authorities said in many cases they were kept in the dark about the alleged scam.

Some of the parents spent between $200,000 to $6.5 million to ensure that their children received guaranteed admission at the schools of their choice, John Bonavolonta, FBI special agent in charge, said.

"Their actions were, without a doubt, insidious, selfish and shameful," he added.

The scheme's mastermind, William Rick Singer, pleaded guilty Tuesday afternoon to charges of racketeering conspiracy, money laundering conspiracy, conspiracy to defraud the United States, and obstruction of justice.

"I am absolutely responsible for it," Singer, 58, 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."

William "Rick" Singer leaves federal court after being charged in a nationwide college admissions cheating scam in Boston on March 12, 2019. Brian Snyder / Reuters

Singer, who operated a for-profit college counseling and preparation business, orchestrated the scheme and helped torpedo it when he agreed to wear a wire and cooperate with investigators, authorities said.

"In retrospect, looking at everything that occurred, he is remorseful and contrite and wants to move on with his life," Singer's lawyer Donald H. Heller said outside the courthouse.

Loughlin, best known for her role in the 1980s-90s sitcom "Full House," and Huffman, who starred in the 2004-12 ABC hit show "Desperate Housewives," were charged with conspiracy to commit mail fraud and honest services fraud.

Loughlin and her fashion designer husband, Mossimo Giannulli, agreed to pay bribes totaling $500,000 to bolster their two daughters' chances of gaining admission to the University of Southern California, court papers say. Huffman and her husband, actor William H. Macy, paid $15,000 to get one of their daughters unlimited time for her SAT test, prosecutors say.

The FBI recorded phone calls involving the celebrities and a cooperating witness, according to the criminal complaint.

Loughlin allegedly told the cooperating witness that she would arrange for one of her daughters to be photographed on a rowing machine to bolster the false claim on the application to USC that her daughter was the crew coxswain for the L.A. Marine Club team, according to court papers.

In an email, Loughlin allegedly agreed to keep the acceptance of her daughter and the scheme "hush hush."

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Loughlin was out of the country for work when FBI agents arrived at her home Tuesday morning. She was scheduled to return to Los Angeles from Canada late Tuesday, and is expected to surrender to federal officials sometime in the next 24 hours, according to law enforcement sources.

Elizabeth Much, a representative for Loughlin, told NBC News she had no comment.

In addition to putting up $15,000 to get her daughter more time on the SATs, Huffman also explored a plan to boost the test scores of a second daughter, according to court papers.

In a recorded call Feb. 19, Huffman discussed the possibility of having a ringer take the SAT exam for her daughter, prosecutors say. But she raised concerns about the discrepancy in scores that could result from her daughter taking the SAT test in March but then allowing someone to take it in her place sometime afterward, court papers say.

"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.'"

Ultimately, Huffman and her husband decided against it, the court papers say. A representative for Huffman did not immediately return requests for comment. Macy has not been charged.

The plot involved students who attended or were seeking to attend Georgetown, Stanford, Yale, the University of California, Los Angeles, the University of San Diego, USC, the University of Texas and Wake Forest University, according to federal prosecutors.

Of the 50 people charged so far, 33 are parents and nine were college coaches. The others were a mix of standardized test administrators, a test proctor and Singer associates, authorities said.

"We believe everyone charged here today had a role in fostering a culture of corruption and greed that created an uneven playing field for students trying to get into these schools the right way through hard work, good grades and community service," Bonavolonta said.

Prosecutors said the the central figure in the scam was Singer, the founder of The Edge College & Career Network, LLC, also known as “The Key," based in Newport Beach, Calif.

Parents paid Singer $15,000 to $75,000 per test for someone else to take the SAT or ACT exams in place of their college-age sons or daughters, according to the court papers.

Singer facilitated the cheating by advising students to seek "extended time on the exams, including by having their children purport to have learning disabilities in order to obtain medical documentation that ACT, Inc. and the College Board typically required before granting students extended time," the indictment says.

Prosecutors said Singer used the cash to bribe two people who administered the exams — Igor Dvorsiky, of Los Angeles, and Lisa "Niki" Williams, of Houston.

In exchange for receiving the payments, Dvorsiky and Williams allowed Mark Riddell, a Florida man hired by Singer, to secretly take the tests or to replace the children's answers with his own, according to the indictment.

Riddell was paid roughly $10,000 per test, money that was often funneled through a charity account set up by Singer, the indictment says.

From 2011 to last month, parents paid Singer roughly $25 million to bribe coaches and university administrators to "designate their children as recruited athletes, or other favored admissions categories," according to the court papers.

In some cases, Singer’s associates created fake athletic "profiles" in an effort to improve the students' chances of getting accepted by making them appear to be highly successful high school athletes.

Singer would then bribe college coaches to allot slots meant for incoming athletes to the children of the wealthy parents, authorities said.

In one of the most egregious cases outlined in the indictment, a set of parents agreed to pay Singer $1.2 million to get their daughter into Yale. Singer set the plot in motion in November 2017 when he passed along the applicant's biographical information to an associate and instructed her to create a bogus athletic profile, court papers say.

"[C]ould you please create a soccer profile asap for this girl who will be a midfielder and attending Yale so she has to be very good," Singer wrote, the indictment says. "...Need a soccer pic probably Asian girl."

The fake profile was sent to the Yale women's soccer coach Rudolph "Rudy" Meredith, who agreed to designate the young woman as a team recruit even though he knew she did not play competitive soccer, according to the court papers.

After the applicant was accepted to Yale, Singer sent Meredith a check for $400,000, drawn on an account belonging to his purported charity, the Key Worldwide Foundation.

Meredith, 51, was charged Tuesday with conspiracy to commit wire fraud and honest services wire fraud. He could not be reached.

Yale President Peter Salovey noted in a letter to students and staffers that Meredith no longer works at the university.

"We do not believe that any member of the Yale administration or staff other than the charged coach knew about the conspiracy," Salovey said.

The coaches charged in the scheme also include Jorge Salcedo, a former professional soccer player who coached the UCLA's men's team, and William Ferguson, who was the women's volleyball coach at Wake Forest. They were not immediately available for comment.

Word of the indictments sparked swift action at some of the schools. Stanford fired its head sailing coach, John Vandemoer, after he was charged with racketeering conspiracy. The school noted that neither of the two students, whom Vandemoer is alleged to have recommended for admission, came to Stanford.

USC said it has terminated the employment of Donna Heinel, the school's senior associate athletic director, and Jovan Vavic, its former water polo coach, after they were indicted in connection with the alleged cheating scam.

UCLA, meanwhile, said it placed Salcedo on leave while the matter is under review.

"The conduct alleged in the filings revealed today is deeply disturbing and in contrast with the expectations we have of our coaches to lead their teams with honesty and integrity," UCLA said in a statement. "If the facts alleged are true, they represent a grave departure from the ethical standards we set for ourselves and the people who work here."

Besides the actresses, other parents implicated in the fraud include Gamal Abdelaziz, the former president and CEO of Wynn Resorts Development; Gordon Caplan, co-chairman of the law firm Willkie Farr & Gallagher LLP; and Gregory Abbot, CEO of the International Dispensing Company. They did not respond to requests for comment.

The investigation involved more than 200 federal agents who fanned out across six states. The probe was launched last May after agents uncovered evidence of "large-scale fraud" while working on a separate undercover investigation, the FBI's Bonavolonta said.

"Following 10 months of intense investigative efforts using a variety of sophisticated techniques, the FBI uncovered what we believe to be a rigged system," Bonavolonta said, "robbing students all over the country of their right at a fair shot to getting into some of the most elite universities in this country."