GRAND RAPIDS, Mich. -- A former Michigan State University and USA Gymnastics doctor pleaded guilty Tuesday to possessing child pornography, admitting he tried to get rid of the evidence last fall while police were investigating allegations that he had sexually assaulted young female athletes.

Dr. Larry Nassar pleaded guilty to three charges in federal court in western Michigan, each of which could land him in prison for up to 20 years.

He is awaiting trial on charges in three separate cases alleging that he sexually molested a total of nine girls, including eight who were gymnasts seeking treatment for injuries. He has pleaded not guilty, and his attorney, Shannon Smith, said Nassar intends to proceed to trial in those cases.

"The plea was negotiated only to resolve the federal charges," she said, referring to the child porn case.

Investigators in September discovered that Nassar's hard drives with thousands of illicit images had been thrown in the trash, as women and girls -- mostly former gymnasts -- were coming forward and saying he had molested them during appointments. Some allegations go back to the 1990s.

Nassar, 53, acknowledged that he dumped the hard drives and paid $49 to have a laptop computer wiped clean to "impede and obstruct" investigators.

As part of the plea deal, the government said it won't prosecute Nassar for travelling internationally between 2006 and 2013 with the intent of engaging in sexual conduct with minors.

Nassar was a sports medicine specialist at Michigan State, especially in treating gymnasts in the region. He also worked for Indianapolis-based USA Gymnastics, which trains Olympians.

Nassar's career began to collapse last summer after the Indianapolis Star reported how USA Gymnastics mishandled complaints about sexual misconduct involving the doctor and coaches.

Women and girls said they felt empowered to speak up after the newspaper published stories.

In addition to the three pending criminal cases in Michigan, Nassar is being sued by more than 100 women or girls who have made similar claims against him.