When it came to getting their daughters into college, actress Lori Loughlin and fashion designer J. Mossimo Giannulli were taking no chances.

The wealthy, glamorous couple were determined their girls would attend USC, a highly competitive school that offers seats only to a fraction of the thousands of students who apply each year.

So they turned to William Singer and the “side door” the Newport Beach businessman said he had built into USC and other highly sought after universities. Half a million dollars later — $400,000 of it sent to Singer and $100,000 to an administrator in USC’s vaunted athletic program — the girls were enrolled at the school. Despite having never competed in crew, both had been given coveted slots reserved for rowers who were expected to join the school’s team.

“This is wonderful news!” Loughlin emailed Singer after receiving word that a spot for her second daughter had been secured. She added a high-five emoji.

According to a sweeping criminal investigation into fraudulent college admissions unveiled Tuesday, Loughlin and Giannulli are one of at least dozens of families who paid huge sums to take advantage of Singer’s audacious scheme to gain access to exclusive schools through bribes and lies.

Federal investigators said they have charged 50 people in the case, including the USC administrator who helped Loughlin’s kids, and accomplices whom Singer allegedly paid to rig college admission test scores — as well as coaches at USC, UCLA, Stanford and Yale.

The charges stunned the upper echelons of American academia, heightening debate about the advantages the ultra-rich enjoy in accessing the country’s best colleges amid intense competition in which merit alone is not enough to assure admission, even for students with perfect grade-point averages and stellar resumes. The accusations also raised serious questions about how university admissions officials, athletic departments and others could have allowed such blatant fraud to go undetected.

There was particular upheaval at USC, a campus already reeling from several scandals. Prosecutors alleged that a top athletic department leader as well as three current and former coaches accepted nearly $2 million in bribes to get students into the school.

The case names celebrities, corporate executives, investment bankers, business owners, top-tier lawyers, and even a best-selling author of parenting books. They sought Singer out from different parts of the country, but with one overriding goal: To get their children into the best colleges.

Andrew E. Lelling, the U.S. attorney in Massachusetts, called the defendants “a catalog of wealth and privilege.”

Loughlin and Giannulli face charges, as well as actress Felicity Huffman and 30 other parents accused of hiring Singer to get their children into desired schools.

FBI agents took Huffman into custody early Tuesday morning at her home in Los Angeles. She was led away in handcuffs and taken to a federal holding facility downtown along with 11 others, authorities said. She spent hours in detention before being freed on $250,000 bond during a hearing in a courtroom where her husband, actor William H. Macy, looked on. An attorney for Huffman declined to comment on the charges.

In announcing the charges, Lelling said the yearlong investigation is the largest of its kind in the country and left open the possibility that charges against more people could follow.

Singer, 58, pleaded guilty Tuesday in a Boston courtroom to racketeering and other charges as part of a plea agreement with prosecutors. He admitted to collecting more than $25 million between 2011 and February this year in a two-pronged scheme in which parents could pay tens of thousands of dollars to have an expert test-taker on Singer’s payroll take their children’s college admission tests or write larger checks to buy spots that colleges reserve for athletes.

A law enforcement official familiar with the probe but not authorized to discuss it publicly said federal authorities had gone to several prominent high schools in Southern California seeking records related to students whose parents were believed to have hired Singer.

In phone conversations with parents secretly recorded by agents, Singer boasted he had helped more than 850 students of the wealthy and powerful to lie their way into colleges in just two years. Lelling said that in some of the cases known to investigators the children were aware of the con carried out on their behalf, but that others were kept in the dark by their parents.

This was a case, said Joseph R. Bonavolonta, special agent in charge of the FBI in Boston, in which parents “flaunted their wealth, sparing no expense, to cheat the system so they could set their children up for success with the best education money could buy, literally.”

Singer, who owns a college preparation company, ran his ploy through Key Worldwide Foundation, a charity he started in 2012, prosecutors said in court papers. The organization’s mission was “to provide education that would normally be unattainable to underprivileged students,” according to paperwork.

In reality, however, Singer used the foundation to collect payments from parents and pay bribes, court records show. Because they were writing checks or, in at least one case transferring stock in Facebook, to a charity, parents were able to write off their payments to Singer as tax deductions, Lelling said.

Parents who worried their children would not score high enough on standardized tests were charged between $15,000 and $75,000 to put their fears to rest, according to court records.

Singer instructed parents to petition for their children to be designated as having special needs that required them to be allotted additional time to take the exams. In at least one instance, a student claimed to have a learning disability to obtain medical documentation required to grant the extra time.

Then Singer would pay a contact at a private school in West Hollywood or one in Houston to arrange to administer the tests to students. For the exams, Singer would fly out Mark Riddell, who worked as a college testing instructor in Florida. For a fee, Riddell would either simply take the exam for the student or correct answers afterward, Lelling said.

Riddell, 36, Igor Dvorskiy, 52, the director of the West Hollywood College Preparatory School, and Niki Williams, 44, a college test administrator in Houston, have all been charged in the case.

Huffman, who garnered fame from her role on the TV show “Desperate Housewives,” and her husband, actor William H. Macy, paid Singer $15,000 last year for a high SAT score Riddell orchestrated for their daughter, according to a criminal complaint filed against Huffman that alleges conspiracy to commit mail and wire fraud. Macy has not been charged, although investigators said in an affidavit that he joined his wife for a meeting with Singer at which the testing scam was discussed.

Riddell got the girl a score of 1420 on the 1600-point SAT exam, according to an affidavit filed by an FBI agent in the case. It was a 400-point jump over what she had scored on an earlier test — an improvement purposefully calibrated by Singer to impress college admissions officers but not so large as to draw suspicion, authorities said.

“He didn't have inside information about the answers, he was just smart enough to get a near-perfect score on demand or to calibrate the score,” Lelling said of Riddell.

Huffman, who told Singer she was interested in hiring him again for her younger daughter but ultimately decided against it, made a brief court appearance Tuesday afternoon. As Macy watched from the gallery, she told a federal magistrate she understood the charges against her and was ordered released on bond.

For larger fees, parents could avail themselves of the contacts Singer built with Donna Heinel, the senior associate athletic director at USC, as well as coaches at USC and other schools who were willing to lie about students’ athletic abilities in exchange for bribes. In some instances, Singer had photos doctored to superimpose the faces of children onto the bodies of athletes. Coaches used the fake images to prove to colleagues that the kids were athletes.

Of the $1.2 million Singer admitted to taking from a family that wanted to go to Yale, $400,000 was paid to the women’s soccer coach, Rudolph “Rudy” Meredith, prosecutors said. The young woman was admitted to the Ivy League school as a soccer recruit despite not playing the sport competitively, according to a court filing.

At USC alone, Heinel is alleged to have accepted $1.3 million in bribes to get a dozen students into the school. Three other current and former members of the athletic department were also charged in the case. After the charges were announced, the university fired Heinel and longtime men’s and women’s water polo coach Jovan Vavic, who is accused of taking $250,000 in bribes. Former USC women’s soccer coach Ali Khosroshahin, who was fired by USC in 2013, and his former assistant coach, Laura Janke, who left the school in 2014, were also named.

To sell the lie that Loughlin and Giannulli’s kids were talented rowers, Singer had Giannulli photograph them both working out on a rowing machine, court documents show. Singer forwarded the photos to Heinel, who used them and other fabrications to sway a selection committee, prosecutors said.

On phone calls captured by investigators and transcribed in court filings, some parents voiced ethical qualms or nerves about getting caught before deciding to press ahead. Others embraced the opportunity with enthusiasm.

“It’s the home run of home runs,” Singer assured Gordon Caplan, an attorney from New York, when he called to to ask about Singer’s test-taking service.

“And it works?” Caplan asked.

“Every time,” Singer replied, laughing.