And the reformed jewel thief, who uses the pseudonym William Steel, claims the couple made him watch some to prove how they "owned" people.
In an exclusive interview with The Sun, the ex-criminal turned writer tells how he was shown footage involving two high-profile US politicians having sex with minors and two high society figures having a threesome with an under-age girl.
Steel — who is not being paid for this interview — also branded Maxwell, 58, who was arrested last week in connection with trafficking young girls, a wild "nymphomaniac" who would try "everything and anything in bed".
He says: "I was forced to watch their videos because they were trying to impress me.
"They wanted to convince me of their power and who they held in their grip.
"They boasted about 'owning' powerful people.
"Ghislaine was more into showing me those than Jeff.
"When you're in a situation like that, you have to pretend to be non-judgmental. But it was shocking.
'IT WAS SHOCKING'
"I saw videos of very powerful people — celebrities, world figures — in those videos having sex, threesomes, even orgies with minors."
In 2018, Steel wrote a bombshell memoir called Sex And The Serial Killer — about his relationship with multi-millionaire suspected serial killer Robert Durst.
He says he included some of what he saw at Epstein's Palm Beach mansion, where Epstein was accused of molesting young girls, but those pages had to be redacted for legal reasons and were never published.
'Jeff had hand in back of young girl's shorts'
He now wants to see Maxwell punished for her alleged crimes.
And he pledged to give all his information to the authorities and testify in court.
He says: "I saw videos and photos of people having sex with various young girls and with Jeff.
"There was footage of two very high-profile society figures and an under-age girl together.
"Two high-profile American politicians were also in different videos with minors.
"They showed me black-and-white footage of a woman they told me was internationally known, a well-known rock star and another man having sex.
"It looked like it was taken in the 1960s and without their knowledge.
"They wanted to impress me and intimidate me. They were so powerful because of who they knew worldwide."
Steel, who stole millions of dollars in art and jewellery across the US, also revealed how Epstein and Maxwell used to buy his stolen goods — even though they were both so wealthy — to give to the girls they were grooming.
He says: "It was mostly tennis bracelets, charm bracelets, women's Piaget watches.
"I remember pearls were a popular thing.
"None of it was for them. They didn't need to buy stolen jewellery.
"They didn't even need to buy stolen jewellery for the girls, but they did.
"They would buy it as gifts for girls they were trying to impress or groom."
Steel revealed how he first met Epstein, who was found dead last August while awaiting trial for sex trafficking charges, in the mid-1990s at a diamond dealer's store in Palm Beach, Florida.
He says: "We were in the upstairs room at a very high-end diamond dealer, the kind of place where only a few people are allowed in at a time.
"I was there doing what I do. I was meeting my fence.
"I saw Jeff with a young girl who looked only about 13 or 14 and he had his hand in the back of her shorts.
"That's what first got my attention.
"She was so young and he was much older. That's when I knew that he was dirty.
"I had about 200,000 dollars worth of jewellery that I was getting rid of and later I struck up a conversation with him.
"He later said the girl he was with was his niece but I called bulls**t on that, telling him I saw what he was doing with her.
"I met Ghislaine at some point later and we were intimate a few times.
"I wouldn't say it was a relationship — it was all about what she could use me for to help them.
"Me being a cocky young guy from New York City, seeing their arrogance and their wealth — I just looked at it as an opportunity to milk them for what I could.
"I used to brag about what I was capable of to them.
"When I wanted to impress or scare somebody, I'd get my briefcase out and it would have police scanners in it, gloves, lock picks, guns with silencers.
"I even owned an ultra-thermic torch which would burn a hole into anything in seconds.
"I'd open the briefcase to show the jewellery and they would see what I was walking around with, so they knew not to double-cross me.
"That impressed Ghislaine and Jeff."
Steel tells how he often saw under-age girls coming and going from their oceanfront mansion on El Brillo Way, Palm Beach.
'SHE TIED ME UP AND HAD SEX WITH ME'
But he adds he was never involved in anything sexual with them and always voiced his disapproval.
He adds: "I only ever had sex with Maxwell and threesomes with her and other adult females.
"I suspected what they were doing with the under-age girls, I knew their routine, so when they tried to get me involved, I said, 'No, I'm not into that — you're not getting me on video doing any of that'.
"One time — it was the second-to-last time I saw them — I was wanted for a serious felony, so to get out of town I went to see them.
"I had planned to just go to their house and steal what I could but then I ended up reconnecting with them and we had sex where she tied me up.
"When it came to sex, she was a nymphomaniac.
"She was into everything and anything."
And while he says Maxwell was very loyal to Epstein, she also knew that one day he would be her undoing.
He explains: "She said to me that she often thought she needed to do something about Epstein, telling me, 'He is going to be the death of me'.
"So while she protected him and helped him, she was simultaneously plotting against him and trying to distance herself.
"She knew they could drag each other down.
"I think she saw herself as the more respectable of the two. She wanted me to do something about Jeff."
He claims Maxwell also confided in him about her "Polanski plan" — named after disgraced film director Roman Polanski, who fled the US after being charged with raping a 13-year-old girl.
He said: "She told me about her Polanski plan where she would flee to France because they couldn't extradite her.
"I was surprised to hear she'd been picked up in New Hampshire.
"I want the authorities to know about her plan before her bail hearing."
Steel remembers how during his last encounters with the pair, in 2005, Epstein and Maxwell seemed to be going through the Palm Beach property and attempting to throw away lots of items.
He said: "They seemed in a scramble to get rid of things like computers, discs, things like that.
'TAKE 100 YOUNG GIRLS TO ISLAND FOR ORGY'
"Doing what he did, crossing the line and potentially blackmailing so many people, he owned people, because of these videos and the pictures he had of them in compromising situations.
"One time Jeff asked me — knowing I had good knowledge of alarms and security systems — if I could see where he had placed his cameras.
"I couldn't find them, they were so well-hidden.
"I knew what he was capable of and I didn't know if they had me on video, not with minors because I never did that, but with her and whatever other weird stuff they were into.
"So I needed a bargaining chip of my own.
"I left with some of those things — discs and things they were trying to get rid of.
"I sent them to the authorities, but I don't know if they did anything with them.
"I don't know what Jeff and Ghislaine did with the rest of them.
"I think they got rid of them before the authorities got their hands on them."
Steel said the pair also asked him to help them find girls — but he refused.
He adds: "Ghislaine was always talking down to people.
"She tried to pull that on me but I told her straight, 'Don't speak to me like you speak to your f***ing staff. I'm doing favours for you guys. You're not talking down to me. I don't give a f how much money you have'.
"They knew I had connections in various places and they offered me money to bring in girls but I never took them up on any of that.
"They told me, 'Whatever the girls want, I can help them with their modelling career if they want that or pay for their education, and it's just massages'.
"And I said, 'Yeah, I'm pretty sure what your massages turn into'.
"And he would just smirk at me and say that I could have what I wanted.
"I said I didn't want that, it's not fair to take advantage of these young girls. It's not right.
"He wanted me to help him with a plan he had to kidnap or pay 100 young girls and take them to an island where he would have sex with them, orgies, use them for blackmail and have babies with them.
"I just told him to shut up. I didn't even realise he was serious until years later.
"For him, at that time, his focus was getting girls that were not from the United States.
"He wanted girls from abroad because he felt they wouldn't know how the criminal justice system in the US works and would be less likely to report him.
"He said he would help look after their families but I said, 'I'm not going to help you ruin a teenage girl's life'.
'I WANT TO RIGHT THE WRONGS I'VE CAUSED'
"I always had to be careful with what I said, though.
"I wanted him to trust me but, equally, I never knew if he was setting me up or taping me. So I had to be careful. It was a fine line."
Steel is now planning to write a book about his experiences with the notorious pair.
He said: "I think the story needs to be told now.
"There are people who have escaped justice for too long.
"You know I was a professional jewel and art thief, stealing millions of dollars of jewellery and art for years, all across the United States.
"It was like an addiction and at the time I loved it.
"I loved that lifestyle . . . until I started going to prison in the 2000s and that's when I had a wake-up call and realised it's not worth it.
"I lost everything that matters.
"I want to turn it around and help people now.
"I want to right the wrongs that I've caused and witnessed and I want to co-operate with authorities on this case so these people can be held accountable.
"I've attended college and they want me to speak to their students and I was humbled when my book was taken to the Sundance Festival.
"I just want to give something back."
Maxwell was arrested in a luxury hideout in Bradford, New Hampshire, last week and charged with conspiring with Epstein to traffic young girls for sex.
She is currently being held at the Metropolitan Detention Center in Brooklyn ahead of a hearing on Tuesday.
That hearing will decide whether she will be granted bail.
Maxwell denies all wrongdoing.
Comment: Not exactly the most stellar source, but what he says matches up with what we know from other sources. It will be up to investigative authorities to see if "Steel" has any actual evidence that can be used against Maxwell. That's assuming the trial will be legit - and that's assuming there will be a trial.