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The abuse Biles and around 149 other female accusers suffered - including Aly Raisman, McKayla Maroney and Maggie Nichols - is well known, thanks to Netflix documentary Athlete A, and news bulletins at the time.
Nassar is serving a life sentence for sexually abusing the athletes under his care.
And speaking to the senate, Simone demonstrated started her powerful testimony by reading a quote from Nelson Mandela.
“There can be no keener revelation of a society’s soul than the way in which it treats its children," the 24-year-old said.
“To be clear, I blame Larry Nassar and I also blame an entire system that enabled and perpetrated his abuse,” she said.
“USA Gymnastics and the United States, Olympic and Paralympic Committee knew that I was abused by their official team doctor long before I was ever made aware of their knowledge.”
Simone was speaking on the incident because the FBI has been accused of failing to properly investigate the gymnasts' and their families' allegations against Nassar - subsequently allowing him to continue his abusive ways.
“Children suffered needlessly because multiple agents in multiple offices at the FBI neglected to share the Nassar allegations with their law enforcement counterparts at state and local agencies,” Republican senator Chuck Grassley told the room.
Simone Biles tearfully acknowledged that the impact of Nassar's abuse was still evident as she took part in the Tokyo Olympics - where she famously withdrew early as a result of her mental health.
“The scars of this horrific abuse continue to live with all of us … I worked incredibly hard to make sure that my presence could help maintain a connection between the failures [around the Nassar case] and the competition at Tokyo 2020,” she said.
“That has proven to be an exceptionally difficult burden for me to carry, particularly when required to travel to Tokyo without the support of any of my family.
"I am a strong individual and I will persevere, but I never should have been left alone to suffer the abuse of Larry Nassar. And the only reason I did, was because of the failures that lie at the heart of the abuse that you are now asked to investigate.”
Telling the panel that she believed similar cases would arise again if action wasn't taken and the FBI and investigating bodies didn't change their ways, and admit wrongdoing, she said: “Nassar is where he belongs. Those who enabled him deserve to be held accountable.
"If they are not, I am convinced that this will continue to happen to others across Olympic sports."
Simone wasn't the only person who spoke out on the FBI's failure.
McKayla Maroney and Aly Raisman also spoke about how they felt their complaints against Nassar fell on deaf ears.
“After telling my entire story of abuse to the FBI in the summer of 2015, not only did the FBI not report my abuse, but when they eventually documented my report, 17 months later, they made entirely false claims about what I said,” Maroney, 25, said. “They chose to fabricate. They chose to lie about what I said and protect a serial child molester rather than protect not only me, but countless others.”
Troublingly, Nassar abused up to 70 athletes after the FBI first learnt about allegations made against him, up until September 2016.
“My reports of abuse were not only buried by [USA Gymnastics and the US Olympic and Paralympic Committee], but they were also mishandled by federal law enforcement officers who failed to follow their most basic duties," 27-year-old Raisman testified.
“I don’t think people realise how much it affects us, how much the PTSD, how much the trauma impacts us … There are times where I feel like I forget what I’m saying. I feel like my mind isn’t working. I feel like I have no energy at all. I’m 27 years old and my 80-year-old grandfather has more energy than I do."
Speaking after the women's statements, FBI director Christopher Wray confirmed: “I want to be crystal clear: The actions and inaction of the FBI employees detailed in this report are totally unacceptable.
USA Gymnastics has now agreed to pay a $215m (£164m) settlement to the athletes who were abused in Nassar's care.
Meanwhile, chief executive of the USA Gymnastics, Li Li Leung, admitted in February that she was aware “how deeply we have broken the trust of our athletes and community", adding that they are "working hard to build that trust back”.
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