A British man has been given 22 life sentences after admitting 71 charges of sex abuse against children in Malaysia aged from six months to 12 years old.
Police believe Richard Huckle, 30, from Ashford, Kent, abused up to 200 children from mainly poor communities.
The Old Bailey judge described a 60-page paedophile manual Huckle wrote as a "truly evil document" and said he must serve at least 23 years in jail.
A woman in the public gallery shouted: "1,000 deaths is too good for you".
In online posts, Huckle had bragged: "Impoverished kids are definitely much easier to seduce than middle-class Western kids."
Commenting on one of his victims, he boasted: "I'd hit the jackpot, a 3yo girl as loyal to me as my dog and nobody seemed to care."
'Such a scale'
He presented himself as a practising Christian and first visited Malaysia on a teaching gap year when he was 18 or 19. He then went on to groom children while doing voluntary work.
The BBC has learned that the National Crime Agency (NCA) only contacted two churches Huckle attended in Kent and London - which cannot be identified for legal reasons - last week, almost 18 months after Huckle was first arrested.
It says it has now referred that aspect of its investigation to the Independent Police Complaints Commission to see if it could have improved its response.
Judge Peter Rook QC said Huckle's sentence reflected the "public abhorrence" over his "campaign of rape".
He said: "It is very rare indeed that a judge has to sentence sexual offending by one person on such a scale as this."
He added that Huckle's life "revolved around your obsession with your own sexual gratification by child sex abuse".
"It is also clear that, had you not been arrested, you planned to continue the same lifestyle using the expertise that you were keen to show off to and share with other abusers so as to continue your sexual exploitation of the children of such communities," he said.
The freelance photographer admitted the offences, which took place between 2006 and 2014.
'Borders are no barrier'
Investigators found more than 20,000 indecent pictures and videos of his assaults on children, which were shared with paedophiles worldwide through a website hidden in the so-called dark web.
He even tried to make a business out of his abuse by crowd-funding the release of the images and was compiling a paedophile's manual at the time of his arrest by the NCA in December 2014.
Australian police, who traced Huckle, also suspected 17 other British men of using the same websites.
Five of those have now been convicted, two have killed themselves, and five have been arrested and are on bail, the NCA said.
One of the men is still being investigated, no further action was taken in one case, and in the final three cases, the NCA said investigators were "unable to resolve IP [internet protocol] data".
Ahead of his sentencing, Huckle claimed to a psychiatrist that he wanted to put his "madness" behind him and settle down with a south Indian woman.
But the court was shown a posting from 2013 in which he outlined his plan to marry one of his victims in order to help him abuse more children.
Judge Rook said: "In my view, you may well harbour feelings of regret but there is no feeling of genuine remorse in this case."
James Traynor from the NCA's child exploitation and online protection command said Huckle had "deliberately travelled to a part of the world where he thought he could abuse vulnerable children without being caught".
"He spent several years integrating himself into the community in which he lived, making himself a trusted figure. But he abused that trust in the worst possible way."
The NCA was able to use legislation that allows UK nationals to be prosecuted in the UK for offences that have been committed overseas.
"The NCA worked to track down Huckle and end his prolific abuse. Borders are no barrier - we are determined that those who go abroad to abuse children will be held to account," he added.