Olympic gymnast Simone Biles tearfully said she blames Nassar and also "An entire system that allowed his abuse," including USA Gymnastics and the U.S. Olympic and Paralympic Committee.
"The scars of this horrific abuse continue," Biles testified, saying that "The impact of this man's abuse will never be over." McKayla Maroney said Nassar "Turned out to be more of a paedophile than he was a doctor."
She recalled sitting on her bedroom floor in 2015 telling the FBI on the phone "All of my molestations in extreme detail."
She said that after describing instances of abuse by Nassar, including before she won the team gold medal at the London Olympics in 2012, "I cried, and there was just silence" on the part of the FBI agent.
Advocates for the women say as many as 120 athletes may have been abused by Nassar after the FBI first heard of the charges against him.
Sen. Richard Blumenthal, D-Conn., asked if they knew of other athletes abused by Nassar after the first incidents were reported to the FBI's Indianapolis field office in July 2015.
Sen. Ted Cruz, R-Texas, said that "The system failed you. That system needs to change. That system needs to be held accountable so that this doesn't happen again."
In his opening statement, Senate Judiciary Committee Chairman Richard Durbin, D-Ill., called the FBI's handling of the case "a stain on the bureau."
"In the 15 months that FBI officials shirked their responsibility, Nassar abused at least 70 young athletes," Durbin said.
"For many of them, this was a continuation, but for others, they were abused for the first time while the FBI sat on the case." The four who testified Wednesday, including Maggie Nichols - who was the first to report Nassar's abuse to USA gymnastics in 2015 - are among hundreds of women and girls who said Nassar sexually abused them while claiming he was treating them.
Nassar, who is serving an effective life sentence in prison, has admitted to abusing girls and women who received treatment from him.
