Aly Raisman, a six-time Olympic medalist and two-time national team captain, said she was sexually abused by former Michigan State and USA Gymnastics doctor Larry Nassar, according to CBS' "60 Minutes."

Nassar already faces 22 counts of first-degree criminal sexual conduct and could receive a sentence of life in prison.

Raisman told "60 Minutes," in an interview scheduled to air Sunday, that she spoke to FBI investigators after serving as national team captain at the 2016 Games in Rio de Janeiro. In the interview, Raisman said she didn't know why it took so long for allegations against Nassar to come forward.

Gymnast Aly Raisman won three Olympic gold medals -- and six medals overall -- while serving as national team captain at the 2012 Games in London and 2016 Games in Rio. Jean Catuffe/Getty Images

"Why are we looking at why didn't the girls speak up? Why not look at what about the culture?" she said. "What did USA Gymnastics do, and Larry Nassar do, to manipulate these girls so much that they are so afraid to speak up?"

Now 23, Raisman told "60 Minutes" that she started seeing Nassar when she was 15. She details the abuse in her book "Fierce," which will be released on Nov. 14.

USA Gymnastics said in a statement Friday that Raisman sharing her personal experience took "great courage" and it is "appalled by the conduct of which Larry Nassar is accused."

Raisman, who was also captain of the team for the 2012 Games in London, is the second member of the "Fierce Five" U.S. women's gymnastics team -- and third Olympian overall -- to allege abuses by Nassar. Just last month, Raisman offered her support to McKayla Maroney after she alleged abuse by Nassar dating back to 2009, when she was just 13.

Nassar was involved with USA Gymnastics for nearly three decades as a trainer and national medical coordinator, a role that led him to treat the country's elite gymnasts at four separate Olympic Games.

During the 2017 national championships in August, Raisman declined to get into specifics about whether she was abused by Nassar, but she painted a vivid picture of how Nassar's behavior went unchecked.

"I think that, you just want, you want to trust people and that he was just a disgusting person, he took advantage of so many people's trust," Raisman told The Associated Press and USA Today Sports. "And I think, it just disgusts me he was a doctor. It's crazy. Because when a doctor says something you want to believe him and it's just awful."

USA Gymnastics, in a statement to "60 Minutes," said it was "very sorry that any athlete has been harmed" and that "we want to work with Aly and all interested athletes to keep athletes safe."

More than 140 women are now suing Nassar and his former employer, Michigan State University. The plaintiffs are also suing USA Gymnastics and other defendants. Attorneys for the alleged victims, USA Gymnastics, the school and other parties to the lawsuit are engaged in court-ordered mediation in an effort to reach a settlement. Attorneys have said that more women are expected to join the lawsuits.

It is not known whether Raisman or Maroney are part of those lawsuits.

Nassar has already pleaded guilty to federal child pornography charges and is in jail, awaiting a Dec. 7 sentencing in that case.

He also faces charges in state court in Michigan, largely related to allegations that he digitally penetrated women during medical exams for his own sexual gratification. If convicted on any one of the 22 counts of first-degree criminal sexual conduct, Nassar could be sentenced to life in prison.

In the past, Nassar and his attorneys have defended the intra-vaginal and intra-rectal procedures as accepted medical practice.

Nassar was a trainer with USA Gymnastics as far back as 1986. In 1996, he was named national medical coordinator, a position he held until the summer of 2015. Nassar resigned his position from USA Gymnastics shortly after concerns were raised about his behavior during medical exams.

USA Gymnastics never informed Nassar's employer at the time, Michigan State University, about the circumstances surrounding Nassar's resignation, and he continued to treat patients in Michigan until he was fired by the school in September 2016.

Raisman has called for change within the sport.

"I am angry," Raisman told "60 Minutes." "I'm really upset because it's been -- I care a lot, you know, when I see these young girls that come up to me, and they ask for pictures or autographs, whatever it is, I just ... I can't ... every time I look at them, every time I see them smiling, I just think ... I just want to create change so that they never, ever have to go through this."

Raisman has also called for sweeping changes in leadership, including the removal of the chairman of the board, Paul Parilla. USA Gymnastics hired Kerry Perry as its new president and CEO on Tuesday after president Steve Penny resigned in March after 12 years on the job.

Raisman and Maroney are the highest-profile gymnasts yet to come forward publicly claiming abuse by Nassar. Jamie Dantzscher, a bronze medalist on the 2000 U.S. Olympic team, was part of the initial wave of lawsuits filed against Nassar in 2016.

The list of Nassar's accusers also includes several former national team members. Jeanette Antolin, Jessica Howard and Kami MacKay have all come forward, alleging abuse by Nassar either through the filing of lawsuits or, in the case of MacKay, on social media.

USA Gymnastics launched an independent review of its policies in the wake of the allegations against Nassar in the summer of 2016, following reporting by the Indianapolis Star that highlighted chronic mishandling of abuse allegations against coaches and staff at some of its more than 3,500 clubs across the country.

In June, the federation immediately adopted 70 recommendations proffered by Deborah Daniels, a former federal prosecutor who oversaw the review. The new guidelines require member gyms to go to authorities immediately, with Daniels suggesting USA Gymnastics consider withholding membership from clubs that decline to do so. The organization also named Toby Stark, a child welfare advocate, as its director of SafeSport. Part of Stark's mandate is educating members on rules, educational programs, reporting and adjudication services.

ESPN's John Barr and The Associated Press contributed to this report.