A brave victim exposed the Great Ormond Street Hospital porter who abused children hundreds of times after he saw on Facebook years later that he was "still around kids", a court has heard.
Paul Farrell, 55, has pleaded guilty to a total of 69 offences involving eight victims over a 35-year period.
From 1985 to 2020 he sexually abused victims aged between five and 16 hundreds of times.
Farrell, of Kentish Town, north London, has admitted abusing two boys in the linen room at the world famous children's hospital in central London, where he had a key to the room.
He will also face sentencing for an additional seven charges of possessing indecent images of children.
The sentencing hearing was told how the sister of two men abused by Farrell when they were boys told him she knew about his "dirty little secret" when she bumped into him at a gym near his home several years later.
Farrell persuaded the children's parents to let him babysit, before grooming the children with sweets and McDonald's food.
He also took his victims to the hospital on the pretext of work experience, the court heard.
Other offences took place in the victims' homes in London and Essex, as well as at a caravan in Kent, and a community centre.
Prosecutors said Farrell's crimes amounted to at least 560 instances of abuse. The oldest victim is now 43-years-old, the youngest victim is just nine.
The victims were not patients at the hospital, Wood Green Crown Court was told.
The sexual abuse survivors were given pseudonyms of alphabetical letters during the sentencing hearing to protect their identities.
Paul Douglass, prosecuting, said: "The first person to make allegations against the defendant to the police was ‘A’ who is now 43 years old…
"A's partner tells of how in the summer of 2019, A saw something on Facebook that made him very angry.
"It appears he had seen a photograph of the defendant – something showing that the defendant was, in his words, still around kids.
"It was this chance occurrence that eventually led to the unravelling of the defendant’s sexual abuse of children spanning 35 years.”
The court heard A's sister remembered how her brother, known in court documents as B, told her in 2006 that he was sexually abused by a babysitter when he was five to seven years old but refused to name the culprit.
In late 2019, A's sister bumped into Farrell in a gym in Kentish Town, the prosecutor said, and remembered him in his 30s playing football with her brothers in the mid-90s when she was around eight to 10 years old.
Douglass said A's sister confronted Farrell in the gym and after finding out he was an employee at Great Ormond Street, she phoned police on 16 November 2019 and reported what her brothers had said.
It was only after the two brothers made formal complaints in January 2020 that Farrell was arrested and various devices were seized, including a phone that contained incriminating texts.
The sentencing hearing continues.
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