An expert who advised on how to protect children from paedophiles has been jailed for seven years for the "systematic abuse" of three young girls.
King kept a diary of the sexual abuse
Stephen King, 54, who also recommended sentences for child abusers, had sex with a 10-year-old, a court heard.
King, of Herne Hill, south London, pleaded guilty to 21 counts, including sex with a girl under 13, and 10 cases of indecent assault.
He was also convicted in 1989 for gross indecency, serving six months in jail.
He had taken 500 photographs, and kept a diary of each sexual encounter.
He kept a video showing acts of indecency with the girls, which took place between October 1996 and the end of 1999.
The three girls were aged between nine and 13 years old.
Peter Zinner, prosecuting, said all three victims had been deeply traumatised by the experience, with one attempting suicide by taking an overdose and slashing her wrists with broken glass.
Passing sentence, Judge Fabyan Evans said: "It was depraved, corrupt and persistent behaviour on vulnerable young girls."
The Metropolitan Police made a nationwide appeal for any other possible victims of King to come forward.
Speaking outside court, Detective Inspector Neil Thompson said: "Stephen King, in my view, is a devious predatory paedophile who's preyed on vulnerable children in this country for over three decades."
Mr Zinner told Middlesex Guildhall Crown Court that King portrayed himself as an expert in child protection and had conveyed his "expertise" to the Crown Prosecution Service, Metropolitan Police and other agencies.
He was even credited in the final recommendations in the Court of Appeal on offering advice on sentences for paedophiles.
"Behind that veneer of respectability there was a dark secret," said Mr Zinner.
Mr Zinner described the video as unique because "it is the first time that the police have an actual record of a paedophile grooming and conditioning a child and then committing acts of sexual abuse".
Investigations into King began in July last year when officers arrived at his home on suspicion of benefit fraud.
While at the property, one officer saw pornographic material by the defendant's computer.
Police then discovered King had been convicted in 1989 - under a different name - of gross indecency as well as making indecent material and was sentenced to six months in jail.
King was also investigated in 1999 on suspicion of indecent assault against the three girls involved in this case, but not enough evidence was found to prosecute.
William Nash, defending, said King was fully remorseful and hoped to be able to apologise to the girls one day.