Investigators have received about 50 complaints against a former Michigan State University doctor facing three sexual assault charges, officials said at a press conference Tuesday afternoon.

"This is just the tip of the iceberg," Michigan Attorney General Bill Schuette said.

Nassar, 53, who spent decades working with local gymnasts and members of the U.S. women's national team, was arraigned Tuesday on three counts of first degree criminal sexual conduct with a person under 13. The charges carry a maximum sentence of life in prison.

The charges involve a single victim who was neither a patient nor a gymnast, Schuette said.

"Just a child, a little child," he said. The victim is now an adult, and willing to testify against Nassar, he said.

"She provides fortitude to every woman, every girl and every daughter," he said.

Up to 18 investigators have been handling complaints made against Nassar, which began rolling in Aug. 29, said MSU Police Chief James Dunlap.

Schuette said his office is also working with FBI officials and the U.S Attorney's office in Grand Rapids as part of the investigation, which is ongoing. He encouraged people who believe they may have been victimized by Nassar or who have information regarding the doctor to call 844-99-MSUPD.

Schuette refused to say whether additional charges could be expected, or in which jurisdictions those charges could be filed.

Earlier Tuesday, 55th District Court Magistrate Mark Blumer set Nassar's bond at $1 million, saying the allegations involved "clear predatory behavior."

Nassar has since posted 10% of the bond, Schuette said. He surrendered his passport and must submit to GPS monitoring as part of his bond conditions.

"Dr. Nassar stole this victim's childhood which can never be undone," Schuette said. "As a father that thought is heartbreaking. Today's charges are the first step toward providing long overdue justice for this victim and will take someone who appears to be a predator off the streets."

The alleged abuse took place at Nassar's home in Holt between 1998 and 2005, according to court records.

Officers with Michigan State University Police and Michigan State Police took Nassar into custody Monday.

Matthew Newburg, Nassar's attorney, declined to comment after Tuesday's arraignment.

Nassar is at the center of a burgeoning scandal that has unfolded since the Indianapolis Star published a report in August detailing how USA Gymnastics has handled sexual abuse complaints stretching back decades.

He served as the organization's team physician during four Olympic games and was a professor in MSU's College of Osteopathic Medicine, as well as a team physician for the MSU women's gymnastics and women's crew teams.

Nassar left USA Gymastics last fall with little notice. The university fired him in September after receiving a number of sexual assault allegations.

Nassar also worked as a team physician at Twistars Gymnastics Club USA and Holt High School. Holt school officials have said they've cut off that relationship and that Nassar hasn't had contact with students this year. John Geddert, owner of Twistars, declined to comment on the issue last month.

MSU officials have said Nassar wasn't fired specifically because of the allegations, but rather because he failed to comply with "performance requirements" put in place after officials investigated a complaint filed in 2014 by a former MSU student that alleged "abuse during a medical procedure."

Officials did not find any violations of MSU policy during the university's investigation into the incident, and no charges were filed.

Numerous former patients — officials have not said how many — came forward with allegations against Nassar after an Indianapolis Star report detailing the accounts of two women who claim he sexually assaulted them during medical examinations.

Multiple lawsuits also have been filed against USA Gymnastics, including one filed last month that claims the organization and former national team coordinators Bela and Martha Karolyi concealed abuse at their training facility in Texas.

USA Gymnastics earlier this month hired a former federal prosecutor to review its handling of sexual misconduct allegations.

Nassar's attorneys have previously said their client “never denied that he used medical techniques involving vaginal penetration” and provided police with information about the techniques.

“Any allegations that Dr. Nassar was performing these procedures for any purpose other than proper medical treatment are patently false and untrue,” attorneys said in the statement released in September.

Despite the allegations, Nassar received more than 2,700 votes in the race for Holt school board — about 21% of the total. It wasn't enough to win a seat, and Nassar told the State Journal before the election he was no longer pursuing the position. His name still appeared on the ballot because the deadline to withdraw had passed.