(CNN) Federal prosecutors have been sending so-called target letters to people associated with the college admissions scandal, a law enforcement official with knowledge of the investigation confirmed to CNN.
People who have received them include students, graduates and other adults, and they are not all related to the same charge, the official added. The official wouldn't confirm whether the students or graduates are related to the parents already charged in the case or if they are new potential defendants.
Actresses Lori Loughlin and Felicity Huffman are among the high-profile figures caught up in the scandal, which has embroiled dozens of wealthy parents, college coaches and standardized test administrators. Prosecutors say some of the parents facilitated cheating on the SATs and ACTs on behalf of their children, and some parents bribed college coaches to smooth their children's path into college.
The target letters have been sent by the government since mid-March, when the case was first unsealed.
The Wall Street Journal and The New York Times first reported prosecutors' use of these letters.
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These kinds of letters are standard in white collar cases, according to the official. They are used when prosecutors may not have all the evidence they need or they are not ready to arrest those who have received them. Other times, it brings recipients to the negotiating table more quickly than had they not received one.
In this case, the target letters could help prosecutors avoid arresting a young adult, according to the source.
As CNN has previously reported, more arrests are still expected in the scandal, and those arrests are said to include students.
The scam was first uncovered in March, when prosecutors unsealed indictments and criminal complaints charging wealthy parents, college coaches and administrators as part of a fraud to buy their way into some of the most prestigious universities in the country, prosecutors said. In all, 50 people were charged in connection with the scandal.
The mastermind of the plot was William "Rick" Singer, the head of his own company and sham charitable organization that got wealthy students higher scores on the ACTs or the SATs by helping them cheat. Singer would enlist the help of his standardized test-taking guru, Mark Riddell, to take the exams for students or correct wrong answers, prosecutors said.
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In other instances, Singer would bribe college coaches and athletic officials to list wealthy students as new recruits for sports teams. Singer and those coaches knew those students were not competitive players, even going so far as to create fake profiles for them, prosecutors said.
"All of these things, and many more things, I did," Singer said as he pleaded guilty in March. "I created a side door that would guarantee families would get in."
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Huffman was among 13 parents who chose to plead guilty last week to a charge of conspiracy to commit fraud. In exchange for the guilty plea, prosecutors said they will recommend a period of incarceration at the "low end" of the sentencing range and will not bring further charges against her.
Loughlin and her husband, Mossimo Giannulli, pleaded not guilty to conspiracy to commit fraud and conspiracy to commit money laundering, according to federal court filings entered Monday.
She and 15 other parents who also pleaded not guilty were additionally charged with conspiracy to commit money laundering, a move legal experts called part of the prosecution's "carrot and stick" approach, intended to pressure defendants to plead guilty or face further charges.