(CNN) - On Monday, 13 wealthy parents caught up in the college admissions scam agreed to plead guilty to a conspiracy fraud charge.
Less than 24 hours later, 16 parents who did not agree to plead guilty -- actress Lori Loughlin among them -- were hit with another federal charge.
The back-to-back timing of those major announcements shows that prosecutors are using a carrot-and-stick approach to the defendants, legal experts said. Their goal is to pressure them to plead guilty, and fast.
"The carrot is, 'take a quick plea and get your best shot at a lower sentence,'" CNN legal analyst Elie Honig said. "And the stick is, 'we have additional charges that we'll bring if you don't plead by that date.'"
The prosecution's strategy further illuminates the significant risks Loughlin and other parents are accepting in declining to immediately plead guilty. They already faced up to 20 years in prison on the conspiracy fraud charge, and the added count of conspiracy to commit money laundering is also punishable by up to 20 years in prison.
Honig said it's fairly common in large cases like this to give defendants in-or-out dates that function as deadlines for taking plea deals.
"Your initial set of charges doesn't necessarily include everything you have or everything you're able to prove up," he said. "And sometimes you do have a couple of additional charges that you can hold back as the sort of hammer."
Neama Rahmani, a former federal prosecutor, told CNN the timing of the superseding indictment shows the government is sending a message to parents who have dragged their feet or may be considering defending these cases at trial.
"The government is telling them we hold all the cards here. Truly. So you better get on board because if you want to plead (guilty) months or years from now or you want to take the case to trial, that original offer will not be on the table," he said.
Two actresses, two defenses
The high stakes of the decision is easy to see when comparing the two highest-profile defendants in the case, actresses Felicity Huffman and Loughlin.
Huffman, the "Desperate Housewives" star, agreed to plead guilty on Monday to paying $15,000 to a fake charity associated with scheme mastermind Rick Singer to facilitate cheating for her daughter on the SATs.
In exchange for the plea, prosecutors will recommend incarceration at the "low end" of the sentencing range, a $20,000 fine and 12 months of supervised release. Importantly, prosecutors will not bring further charges.
"I am ashamed of the pain I have caused my daughter, my family, my friends, my colleagues and the educational community. I want to apologize to them and, especially, I want to apologize to the students who work hard every day to get into college, and to their parents who make tremendous sacrifices to support their children and do so honestly," Huffman said in a statement.
In contrast, Loughlin's attorneys have not engaged in substantial plea discussions, according to a law enforcement source familiar with the investigation. Loughlin and her husband, fashion designer Mossimo Giannulli, have not publicly indicated how they plan to plead in the case. CNN has reached out to Loughlin's attorney for comment.
Any recommendations by the government would be determined based on Loughlin's actions, including if she decides to plead guilty before the case goes to trial.
Criminal defense lawyer Arash Hashemi speculated that Loughlin's attorneys are preparing for battle -- or perhaps trying to hold out to see if there are weaknesses in the prosecution's case. Those strategies come with risks.
"It's just like playing poker," he said. "You might lose at the end."
Large scope of evidence
One reason so many parents pleaded guilty already is the apparent strength of the evidence against them.
Prosecutors outlined their "voluminous" evidence on Tuesday in a motion for a protective order in the case against David Sidoo, one of the parents charged in the case. As part of the filing, prosecutors asked that the evidence that they turn over to defendants not be disclosed to anyone else.
The evidence includes: Wiretap and consensual recordings, financial records from banks and other institutions and academic records from both high schools and colleges.
Prosecutors also have emails and other electronic evidence obtained through search warrants, wiretap interceptions and subpoenas; surveillance photographs; legal process, including wiretap orders and search warrant affidavits; and other records obtained through grand jury subpoenas.
Rahmani described it as an "indefensible" case because of that overwhelming evidence.
"It's not surprising that so many of these parents pled and pled immediately because this was the best possible deal and it will just get worse over time," he said. "The ones that are foolish enough to try to defend the case, either privately or even publicly in the media, this is going to end badly for them."
CNN's Mark Morales and Kristina Sgueglia contributed to this report.
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