Sadistic Dennis McGrory was 28 when he sexually assaulted, stabbed and strangled Jacqui Montgomery, 15, in her home in 1975. McGrory was charged with murder but was cleared by a jury on the directions of a judge a year later.
Justice caught up with the killer, now 75, after advances in forensic science produced a one-in-a-billion DNA match from swabs taken from the victim’s body.
Jurors took less than an hour to convict him of rape and murder.
On Friday, Jacqui’s sister Kathy Montgomery was at court to see the monster jailed for life with a minimum custody term of 25 years in the oldest double jeopardy case in England and Wales.
If he survives, he will be 100 before he can be considered for release on parole.
Ms Montgomery told reporters: “I’m just relieved. I don’t know what to do with myself, it’s taken so long.
“She suffered, that girl – she didn’t deserve what she got – but he deserved what he got just now.”
Asked how she felt about McGrory being at large for so long, Ms Montgomery said: “Soul-destroying. Soul-destroying, knowing I could do nothing to get near him.
“We all knew he’d done it since day one.”
Asked what her reaction was when Dennis McGrory was jailed, Jacqui Montgomery’s sister Kathy said: “Overjoyed is an understatement.
“Overwhelmed. I never took my eyes off him in that court.
“He knew he’d done it, why didn’t he plead guilty? He’s put all our family through this.
“My mum and dad would have been overjoyed but it destroyed my father. It destroyed him.”
McGrory, who has never shown any remorse, had been “wild with rage” when he murdered Jacqui as he tried to track down his ex-partner Josie Montgomery, Jacqui’s aunt.
During the attack, he ripped out a page of the teenager’s diary with her aunt’s address on it.
Jacqui’s body was found by her father, Robert Montgomery, lying on the floor of their living room in Islington, north London, in the early hours of June 2, 1975.
She had suffered fatal stab wounds as well as blunt force trauma to the face and been strangled with the flex of an iron.
McGrory had threatened to rape Jacqui in the past and, on that night, he “made good” on those words, jurors were told.
In a moving impact statement read to Mr Justice Bryan at Huntingdon Crown Court, Cambs, her sister Kathy said: “A violent man who had been living within our family raped and murdered my sister. He has been able to live his life. He has spent nearly 50 years as a free man doing as he pleased.
“I find that unbearable when my sister didn’t even reach her 16th birthday. His actions caused trauma to so many people and there were no consequences for him.
“The investigation of the last few years has meant revisiting memories of the murder which has caused pain and stress for me and my family and I am relieved that we finally have justice for Jacqui.”
Sentencing McGrory, who appeared at Huntingdon Crown court via video-link from HMP Peterborough, Mr Justice Bryan told him: “I have no doubt whatsoever that you intended to kill her in your brutal attack on her.
“You put Jacqui through a horrific, violent and sustained ordeal in her own home – a place where she was entitled to feel safe.
“In the decades that followed, you must have thought you had gotten away with your hideous crimes.
“How any man could inflict such sexual violence on a 15-year-old child that had done them no harm beggars belief.
“You have shown not one iota of remorse or compassion for Jacqui or Jacqui’s family.
“You cut short that life and deprived her of that life, and all the things she hoped for in that life.”
McGrory’s retrial, in March, was halted when the defendant, of Milton Keynes in Buckinghamshire, fell ill.
He appeared for his retrial at Huntingdon Crown Court by video-link and was found guilty of rape and murder last Mondayyest.