BOSTON – The Justice Department's historic "Varsity Blues" college admissions bribery case is entering a new phase in Boston federal court as sentencing begins this week for the first of 19 parents, coaches and other defendants who pleaded guilty to felonies.

Three others have agreed to plead guilty and await hearings. The 28 defendants who pleaded not guilty are digging in for trials that would play out for many months.

It's been a blockbuster case since it was unsealed in March: famous actresses, CEOs, wealthy investors and other rich parents are accused of paying bribes to the scheme's mastermind, Rick Singer, a college consultant, to get their children accepted into elite colleges. He offered them two tracks: Have someone cheat on their children's ACT or SAT tests, or falsely classify them as athletic recruits.

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Inside the courtroom, prosecutors sought to make a complicated legal argument that the parents' $25 million in total payments to Singer's sham nonprofit group were crimes – mail fraud. They argued that the coaches and test administrators committed racketeering.

Big questions remain: How many additional parents will plead guilty? How many more parents and others could be charged? Will judges come down hard or light with their sentences?

Here are eight takeaways from what we've seen:

Felicity Huffman and Lori Loughlin: One actress gives in as another digs in

The case garnered huge attention from the get-go not only because it exposed a plot for the super wealthy to buy college access – in an unprecedented scope – but because of two names: actresses Felicity Huffman and Lori Loughlin.

A tearful Huffman, who starred in "Desperate Housewives," pleaded guilty last month to conspiracy to mail fraud charges for paying Singer $15,000 to have someone correct SAT answers for her oldest daughter.

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Loughlin and her husband, fashion designer Mossimo Giannulli, pleaded not guilty to allegations they paid $500,000 to Singer for their daughters to be classified as athletic recruits to get them accepted into the University of Southern California. Because they did not agree to deals with prosecutors, they're among the parents who face a money laundering charge.

As a result of her plea agreement, prosecutors recommended four months of prison for Huffman out of a maximum penalty of 20 years of incarceration.

The charges facing Loughlin are more serious – and the potential sentence more severe – given the substantially higher dollar amount. Singer charged parents more for the recruitment scheme than the test cheating.

Loughlin could have other legal issues as well. In a letter attached to court documents this week, her attorney said that USC's legal counsel raised the possibility of a legal dispute with Loughlin and Giannulli.

More:USC hints at lawsuit with Lori Loughlin, Mossimo Giannulli in massive college scheme

Defendants are split

Just as the case's two celebrity defendants have taken different paths, so have the others facing charges. No concrete pattern has emerged to explain why some defendants have pleaded guilty and some haven't.

Parents accused of paying to have someone take their children's test have been slightly more likely to plead guilty than those accused of taking part in the recruitment scheme. But both camps are represented among the guilty pleas.

Among the parents who pleaded guilty, eight participated in the test cheating scheme, five admitted to taking part in the recruitment scheme, and one parent took part in both.

The majority of the remaining 19 parent defendants are accused of taking part in the recruitment scheme. There are four accused of participating in the test cheating scheme and four accused of taking part in both tracks.

Five college coaches accused of accepting bribes pleaded guilty, and four other coaches, two test administrators and the head of a Houston tennis academy pleaded not guilty.

Through plea agreements, the prosecution has methodically gotten more defendants to plead guilty, from four – including Singer, when indictments were unsealed March 13 – to 22.

Most face damaging evidence, including wiretapped phone conversations they had with Singer.

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Define 'bribe'

Defense attorneys of the 19 parents fighting charges signaled what could be a central argument if they go to trial – that parents didn’t know where their money went when they paid Singer.

Singer collected their payments as “donations” to his sham nonprofit Key Worldwide Foundation. Prosecutors said he funneled the money to co-conspirators, including coaches, test administrators, proctors and others. Payments to coaches often went to athletic programs or clubs they controlled.

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In court last week, Aaron Katz, an attorney for Elizabeth Henriquez – a California mother accused of paying bribes of $400,000 to get her two children into college – referred to an email that he said suggests prosecutors spoke to other parents who paid Singer but have not been charged.

"They told the government (that) Rick Singer told them that their money was going to go to athletic programs or schools, not to bribes," Katz told a federal magistrate at an initial status conference hearing.

He said, "That goes to the heart of the honest services charge – a bribe in exchange for the breach of their fiduciary duty."

The government has pushed back at that argument. "It doesn’t matter whether the money went to a coach’s program or the coach directly (for it to be a bribe)," Assistant U.S Attorney Eric Rosen told the judge. He called the transaction a "quid pro quo” regardless.

Singer's extended network

In May, the mother of a Chinese student enrolled at Stanford University confirmed paying $6.5 million to Singer.

The payment from the mother of Yusi Zha, made in 2017, points to Singer's network extending beyond the 33 wealthy U.S. parents, primarily in California, accused of paying him large sums of money to get their children into elite U.S schools.

More:Mom from China who paid $6.5M to Rick Singer says Stanford daughter a 'victim' of admissions scam

U.S. Attorney Andrew Lelling mentioned the $6.5 million figure – the most paid by any parent – when prosecutors announced the case in March.

The payment is not mentioned in court documents, and the parents of Yusi Zha, who is no longer at Stanford, have not been charged.

A Hong Kong attorney for the mother said his client was duped into thinking she was making a donation to Stanford. He said she is a victim of Singer's plot.

3 million pages of evidence

Defense attorneys are sifting through the evidence that the government handed over last month – and there’s a lot of it.

It’s contained in a hard drive and an accompanying DVD that is not available to the public. The evidence spans 3 million pages, including 1 million pages of emails, 4,500 separate wiretapped phone conversations and extensive bank records and other documents kept by Singer.

It’s so voluminous that the defense is struggling to find the portions relevant to their clients. Rosen told the judge that one defense attorney asked for more indexes. “We’ve tried to make it as easy to streamline as possible," he said.

More information is likely to be released periodically.

Most of the defendants who pleaded guilty did so before their lawyers had a chance to look at the evidence. That’s a reflection of the damaging details highlighted in the charging document, thanks largely to the cooperation of Singer, who got many of his clients to restate their transactions by phone while FBI investigators listened in.

Cooperation keeps growing

As they reached plea deals with defendants, the prosecution also got cooperation agreements from six defendants to assist in the FBI's investigation into the college admissions scandal.

The government already had cooperation from Singer and former Yale women's soccer coach Rudy Meredith before prosecutors announced the case.

In recent weeks, Singer's accountant Steven Masera, former USC women's head coach Ali Khosroshahin, former women's soccer assistant coach Laura Janke and parents Davina and Bruce Isackson signed cooperation agreements.

Donna Heinel, former senior associate athletics director at USC, pleaded not guilty.

The cooperation agreements could complicate the cases of defendants tied to USC, and they could lead to others being charged.

The Wall Street Journal, citing unnamed sources, reported that federal investigators are looking at whether former USC athletics director Pat Haden – whose tenure spanned the time when Khosroshahin and Janke were there – was involved in the cheating and bribery scheme.

More:Report: Former Southern Cal AD Pat Haden being investigated in college admissions scandal

Parents might have to pay restitution

In several of the plea agreements made with parents, prosecutors recommended not just prison time but also financial restitution to the Internal Revenue Service or even universities.

One example is Stephen Semprevivo, an executive at the sales company Cydcor, who pleaded guilty last month to charges related to paying a $400,000 bribe to Singer to get his son into Georgetown University as a tennis recruit.

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Prosecutors recommended Semprevivo pay an undetermined amount of restitution to cover Georgetown's attorneys fees even though the university is not a party in the case. That's in addition to 18 months of prison and other penalties recommended.

Bruce Isackson, the head of Bay Area real estate firm WP Investments, pleaded guilty in April to charges of paying more than $600,000 in bribes to get his daughters accepted into UCLA and USC as athletic recruits.

The government recommended 37 to 46 months of prison time and restitution payments to the IRS totaling $139,509. The amount is equal to payments Isackson deducted from his taxes as charitable contributions.

Some of the restitution amounts are not spelled out in the plea agreements. Federal Judge Indira Talwani expressed concern that the lack of specifics could give judges a "blank check" that defendants wouldn't be able to appeal.

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What about the parents not charged?

To help with the defense strategy on what constitutes a bribe, lawyers seek FBI documents known as 302 reports that detail investigators’ interviews with parents not charged in the case.

They sought the records as exculpatory evidence – which the prosecution would be obligated to turn over before trial – but prosecutors resisted.

"We are not going to hand over all our 302s willy-nilly because defendants have some theory about what can be exculpatory," Rosen said in court.

Federal Magistrate Page Kelley denied the defense's request to certify the documents as exculpatory evidence for now, saying she wants to see the case play out.

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