A Harvard alumnus accused of taking SAT and ACT tests for college-bound children of wealthy parents embroiled in a massive admissions cheating scandal is expected to plead guilty to charges of conspiracy to commit mail fraud and money laundering, court documents show.

Mark Riddell, a 2004 Harvard graduate, allegedly secretly took college board exams for students between 2012 and this past February. He was paid $10,000 per test, according to prosecutors.

Mark Riddell IMG Academy

He faces up to 20 years in prison, in addition to supervised release for three years and a $250,000 fine. But the U.S. attorney for the District of Massachusetts said in a court filing that based on Riddell's "prompt acceptance of personal responsibility" for the offenses alleged, prosecutors would recommend a lesser sentence.

Riddell apologized in a statement earlier this month for his role in the scandal.

"I want to communicate to everyone that I am profoundly sorry for the damage I have done and grief I have caused those as a result of my needless actions," Riddell, a resident of Palmetto, Florida, said.

His attorney, Ben Stechschulte, said his client "expressly and unequivocally admits that he committed the crimes" and plans to plead guilty "at the earliest predictable date."

Some other defendants in the case made an initial appearance in federal court in Boston on Monday. The judge saw 12 defendants in batches of three, accompanied by their attorneys.

All 12, who included former university coaches or athletic department staff, pleaded not guilty and are set to appear back in court on June 3.

Among them was Gordon Ernst, a former tennis coach who worked at the University of Rhode Island and Georgetown University, and three former University of Southern California employees - Donna Heinel, Ali Khosroshahin and Laura Janke.

Two of the most high-profile names ensnared in the scandal, actresses Lori Loughlin and Felicity Huffman, are scheduled to appear in court in Boston next month.

Loughlin, best known for her role on "Full House," and her fashion designer husband, Mossimo Giannulli, allegedly agreed to pay bribes totaling $500,000 to bolster the chances for their two daughters, Olivia Jade and Isabella Giannulli, to get admitted to the University of Southern California. Both girls are still enrolled at the school, according to a USC spokesperson.

Loughlin appeared in federal court in Los Angeles earlier this month and was released on a $1 million bond. She and her husband are expected to appear in a Boston federal court April 3.

Huffman and her husband, actor William H. Macy, allegedly paid $15,000 to get one of their daughters unlimited time on the SAT. Huffman is also expected in court April 3.