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Legendary gymnastics coaches Bela and Martha Karolyi — whose training center ranch has been at the center of the Larry Nassar scandal — say there is no way they could have known that the disgraced Olympic doctor was preying on girls on their property.

In an exclusive interview with NBC News, they pointed out that family members who testified during Nassar's sentencing hearings also didn’t know of the abuse.

"Some of the parents were in the therapy room with their own child and Larry Nassar was performing this and the parent couldn't see," Martha Karolyi told NBC News' Savannah Guthrie in an exclusive interview for a special investigative edition of Dateline airing Sunday at 7 p.m. ET/6 p.m. CT.

"How I could see?"

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Over the last year, the Karolyis, now 75, have seen their remarkable legacy called into question because of the sex-abuse scandal unleashed by Nassar, the former Olympics doctor.

Victims were molested at their Texas ranch. They have been named in lawsuits. USA Gymnastics cut ties with them. And some gymnasts have come forward to complain about training methods that created a generation of champions but took an emotional toll.

Through it all, they have stayed silent. Until now.

"The whole thing is just like an explosion, a bomb exploding. Boom," Bela Karolyi said.

The interview took place at their ranch in a forest about an hour from Houston that they purchased in 1983 after defecting from Romania and built into a 2,000-acre compound that hosted gymnasts from around the country.

USA Gymnastics held camps there for the nation's most promising athletes from 1999 until last year, a period in which the U.S. teams achieved Olympic dominance.

As national coordinators, Bela and then Martha oversaw training with techniques that they developed in Romania — where they made history with Nadia Comaneci's perfect 10s — and later made the U.S. standard.

For nearly 20 years, the biggest names in the sport sharpened their skills under Martha's watchful eye: Aly Raisman, Simone Biles, McKayla Maroney, Gabby Douglas, Jordyn Wieber.

Those five 2012 and 2016 Olympians now say they were molested by Nassar, a Michigan physician who volunteered to be the team doctor and claimed putting his ungloved fingers inside them was a legitimate medical treatment.

"That's awful," Martha Karolyi said. "But I would say even if they have big names or they have no names, any child who was violated by Nassar, it's a crime and it's so sad."