Justice has finally come to an east London gardener who raped and sexually assaulted three young victims 25 years ago.

William McMahon, now 60, evaded captured because he was not known to the girls and the forensics were crude failed to identify him.

Now he starts a sentence of 18 years and two months for the rape of a teenager and sexual assault of her two friends in a disused building in east London in 1990. He stole their childhoods, say police. And one of his victims never lived to see McMahon sentenced.

The three friends, two aged 13 and one aged 12, were drawn to the derelict building in Plaistow and went inside to explore. They had no idea they were being followed by McMahon. He accosted them, threatened them and forced them to remove their clothes.

He then anally raped one of the victims, before going on to sexually assault her two companions.

For 20 years he walked free, carrying on a normal life as his victims struggled with theirs. But then the net started to close. In September 2010 a cold case team was put on the investigation. In the intervening decades forensic techniques had advanced and detectives were able to obtain a full DNA profile.

But there was no match in the database. McMahon was not a suspect for another five years. Five years in which the torment of the victims, now in their 30s, continued unchecked. Then in April 2015, the final breakthrough.

McMahon was arrested in connection with an unrelated domestic matter he was at last identified as the mysterious assailant from the disused building.

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A year later, April 2016, at Snaresbrook Crown Court he pleaded guilty to one count of rape, three counts of indecent assault and three counts of false imprisonment.

He was sentenced on Friday, May 6, the unresolved case solved after quarter of a century.

Det Insp Keith Braithwaite, of the Sexual Offences, Exploitation and Child Abuse Command said: “McMahon stole the childhoods of his victims, causing them extreme distress and pain throughout their lives – which continues to this day.

“Perversely, McMahon continued with his life as normal for 25 years.

“I would like to commend the victims for their courage and determination in pursuing this conviction and hope today’s sentence goes some way to bring closure to them and their families for McMahon’s heinous crimes.

“Sadly one of the victims died before he was brought to justice.

“I would like to reassure the public that offences of this nature are thankfully a rarity. The Met will continually review such cases and will use all advances in technology available to bring such offenders to justice.”