He blackmailed young girls, threatening to expose the videos to their families unless they submitted to further sordid demands.
He even convinced one 15-year-old girl in America to molest her own baby sister, who was 10-months-old, to satisfy his perversions, it is understood. Another victim was 2. As Leighton had "coerced" some victims to attack others, it was possible to charge him with rape.
The FBI is expected to try to extradite Leighton for trial in the US after the British courts have finished with him. Today he will be jailed at Newcastle Crown Court after admitting 19 "sample" offences including three rapes, two sexual assaults on girls under 13 and four counts of grooming.
But Detective Sergeant Peter Morgan, of Northumbria Police, told the Mail the true toll was far greater, saying: "Hundreds of families will never recover from the trauma of these offences and will have to live with what he has done to them for the rest of their lives."
He added: "Paul Leighton is one of the most serious offenders I have ever come across and his actions have had devastating impacts across the world. He was calculated and sophisticated in his approach to this abuse and his lack of thought for his victims is spine-chilling."
Leighton was caught after a complaint and his online address was traced. Michael Barton, of Northumbria Police, said: "Unfortunately we live in a world where sick, vile creatures like Paul Leighton take advantage of young children using the internet. He committed these offences on a mobile phone and used the cover of fake social media profiles to carry out abuse that many of us could not even comprehend."
Leighton's former friend Carl Henderson, 36, said: "I heard the FBI raided the house. They were coming out with loads of stuff, computers, laptops, that sort of thing. I'm shocked. I wouldn't think he would be like that. He was in to rave music and would play football with the local lads."
An ex-girlfriend told the Mail that Leighton, who spray-painted cars for a living, used to date single mothers to get access to their children. She said: "He was a creep. He was just aggressive. He was dating women to get at their kids, we think.
"I'd only known him for a couple of months and he would want to take me and my baby son to the beach, but there would be no one else there." She added: "He said he was a computer whizz. He said he knew exactly what to do to fix my computer. But he was weird.
"I was never allowed to meet his parents. It was very specific, I wasn't allowed to speak to anyone, I had to wait in the car. He was seeing my friend for a good few months and she never met his parents either. He was into drugs. He was on weed all the time. The car always smelt of it. He used to drug-drive all the time."
And a neighbour said: "He was a creep. There's something not right in the head with him."
Leighton pleaded guilty at an earlier hearing to three counts of rape, two sexual assaults on girls under 13, four counts of causing or inciting grooming, three counts of making and two counts of distributing indecent photographs, three counts of blackmail, one count of assault on a girl under 13, and one count of possessing a class B drug.