Russell Bishop was 20 years old when he sexually assaulted and strangled nine-year-olds Nicola Fellows and Karen Hadaway in a woodland den in Brighton.
He was originally cleared of their murders exactly 31 years ago but within three years went on to kidnap, molest and throttle a seven-year-old girl, leaving her for dead at Devils Dyke on the edge of the Sussex seaside city.
While serving life for attempted murder, Bishop, now 52, was ordered to face a fresh trial under the double jeopardy law, in light of a DNA breakthrough.
A Pinto sweatshirt discarded on Bishop's route home was linked to the defendant by DNA while fibre, paint and ivy transfers placed it at the scene.
Tests on a sample from Karen's left forearm also revealed a "one in a billion" DNA match to Bishop.
The case, dubbed Babes in the Woods, shocked the nation in 1986 and blighted the tight-knit community of Moulsecoomb, on the edge of the South Downs in Brighton.
It is believed to be the oldest double jeopardy case and Sussex Police's longest-running murder inquiry.
The girls' families gasped and wept in court as the jury delivered its verdict after just two and a half hours of deliberation on Tuesday.
Nicola was a very friendly, outgoing girl who would speak her mind, while Karen was sensible, but could also be cheeky, according to their parents.
Both were afraid of the dark and Nicola's father had banned her from playing in Wild Park, even saying the "bogeyman" lived there, the court heard.
At around dusk on October 9 1986, Bishop spotted the girls playing in the park near their home and seized his opportunity, the prosecution said.
During the attack, he punched Nicola in the face, to "subdue" or "punish" her for being disrespectful to his teenage girlfriend earlier that day, Brian Altman QC suggested.
The prosecutor pointed out Bishop's violent nature, saying he slapped his partner Jennie Johnson when she was pregnant with their second child.
The day after the killings, Bishop joined the desperate search for the children, claiming his dog Misty was a trained tracker.
He was nearby when two 18-year-olds spotted the bodies and rushed ahead of a police officer.
Afterwards, he gave conflicting accounts to police and produced a series of fake alibis, including a "wild man" of the woods and his drug dealer.
He described details of the murder scene which only the killer could have known, including foam around the mouth of one of the girls, the court heard.
In the original trial, the prosecution said the girls must have been killed before 6.30pm, by which time Bishop had been seen heading home on foot and the girls were spotted outside a fish and chip shop.
But in the retrial, jurors heard the time of death could have been later and Bishop simply doubled back to intercept the children, both of whom he knew.
Bishop tailored his defence to the new forensic evidence, claiming he touched the girls to feel for a pulse, even though the 18-year-olds insisted he never got near.
The former roofer denied murder but admitted attacking the girl in 1990 claiming it was because he was angry and wanted to "shame and belittle" her.
Acting on instructions, his defence team cast suspicion on Nicola's father Barrie, suggesting police spent 32 years investigating the wrong man.
During the two-month trial Nicola's father Barrie Fellows, 69, had been reduced to tears over the claims against him.
Bishop's defence also cast doubt on the forensic evidence, suggesting it could have been contaminated.
In his 1987 trial, Ms Johnson denied the blue Pinto belonged to her partner in the witness box, having previous identified it.
In light of the guilty verdict, Sussex Police has refused to rule out investigation her for perjury charges 31 years later.
While Bishop refused to attend court for the verdict, mothers Michelle Hadaway, 61, and Susan Fellows, 69, sat through harrowing evidence for a second time.
Karen's heartbroken father Lee Hadaway died without seeing his daughter's killer brought to justice.
Nigel Pilkington, of Crown Prosecution Service South East, said Bishop is an "extremely dangerous man" who had been convicted on "overwhelming and incontrovertible" evidence.
He said: "He is a violent predatory paedophile and he gets cross when you call him that. He also considers himself to be a victim in the sense of the 1990 conviction."
He said Bishop had tried to blame Nicola's father to create "the most havoc" possible, adding: "There is not a shred of evidence against Barrie Fellows, not realistically at all."
Detective Superintendent Jeff Riley said Bishop was a "wicked" paedophile.
He said: "I still feel it's a shadow over Brighton to this day. I'm very proud of the investigation we have put together. We have been meticulous.
We have never given up on this investigation."