‘Sadistic’ Adam Lewis, 18, tied the 17-year-old college student to a tree, sexually assaulted her, strangled her and attacked her with a knife.
He has now been jailed for at least 22 years for the killing.
Lewis, of Wirral, Merseyside, had denied murdering Miss Windsor but changed his plea to guilty shortly before his trial at Liverpool Crown Court was due to begin.
Final moments: Hannah Windsor, 17, was caught on CCTV walking up Bidston Hill, Wirral, to the campsite of boyfriend Adam Lewis, 18
He also admitted two counts of sexual assault against his victim.
Sentencing Lewis to life imprisonment today, Mr Justice Holroyde told him: ‘Only you know what you did to Hannah and in what order you did it.
‘It is, however, clear that you deliberately inflicted cruel injuries upon her which must have caused her immense pain and suffering.’
Lewis, who has learning difficulties and a low IQ, showed no emotion as the judge told him the pathologist’s report into Hannah’s death made ‘chilling reading’.
Neil Flewitt QC, prosecuting, described Miss Windsor’s injuries as ‘highly distressing’.
She was restrained and tied to a tree, sexually assaulted, stabbed repeatedly and suffered multiple other knife wounds to her chest, abdomen and back, he said.
Sadistic: Defenceless Hannah Windsor, left, was tied to a tree by evil Adam Lewis, right, and subjected to a horrific and sustained attack which continued after her death, Liverpool Crown Court heard
Her mouth had been covered with surgical tape and she was strangled with a combination of his hands and a ligature, Mr Flewitt added.
There were also severe wounds in her genital area and evidence of sexual assaults.
‘The nature and extent of the injuries were such that the pathologist concluded Hannah had been the victim of torture,’ Mr Flewitt told the court.
‘In the pathologist’s opinion, some of the wounds have a sexual component.
‘Some of the injuries were caused after death but some were definitely caused during life.
‘It is entirely possible that at some stage during the process, Hannah died and the defendant did not realise she had died and continued to inflict the injuries.’
During sentencing, the judge added: ‘Adam Lewis, that was a prolonged, merciless and terrible attack, which must have been agonisingly painful for Hannah Windsor before she died.
‘You must have known what dreadful pain you were causing her.’
The judge said Lewis showed ‘dreadful cruelty’ and added: ‘I am quite sure that your murder of Hannah Windsor involved both a sexual and sadistic element.’
Members of Hannah’s family sobbed as they followed proceedings from the public gallery.
The judge said: ‘In every crime of murder, one life is taken but many others are damaged.
‘I have read and taken account of statements by both of Hannah’s parents. They, and other members of her family and friends, have suffered and will continue to suffer as a result of what you did.’
Miss Windsor and Lewis, who were both diagnosed with Attention Deficit Hyperactivity Disorder (ADHD), had met when they were pupils at a Wirral special school.
After leaving school they had been in a relationship for seven months before splitting up and reuniting about six weeks before he killed her, the court heard.
In the days leading up to Miss Windsor’s death Lewis had been hiding from police after a burglary during which he started a fire.
He was sleeping in a tent which he pitched in a woodland clearing on Bidston Hill, a beauty spot on the outskirts of Birkenhead.
Police became aware that Miss Windsor knew where Lewis was hiding and warned her not to go and see him, Mr Flewitt said.
‘Tragically, it seems Hannah was determined to ignore the advice she had been given by police and was intending to visit the defendant at his campsite,’ he added.
Miss Windsor was carrying a note from a detective which contained a phone number for her local police station.
The note was later found torn up at Lewis’s campsite, Mr Flewitt said.
Two days after Miss Windsor disappeared Lewis was found by police sleeping rough at a railway station. A search of the police national computer revealed he was wanted for burglary and arson and he was arrested before being released on bail.
While on bail he told his sister he had killed Miss Windsor and his grandfather contacted police.
Lewis was re-arrested and taken to Bidston Hill where he directed police to an area near where Miss Windsor’s body was found.
Lewis’s previous convictions date from the age of 10 when he committed an offence of dishonesty. Other offences included an assault committed when he was 13, the court was told.
He earlier pleaded guilty to the burglary he committed before he killed Miss Windsor. This will be his third burglary conviction and will result in a mandatory three-year jail term, Mr Flewitt said.
The barrister acknowledged that the burglary sentence will ‘pale in comparison’ to the life sentence he will receive for the murder.
In mitigation, Stephen Riordan QC, defending, said Lewis confessed to the murder last Friday during a meeting with his solicitor.
He maintains he suffered a blackout and cannot recall much of what happened.Mr Riordan said: ‘The time may come, and one hopes it will, when he may face the enormity of what happened. But that time is not yet with us.’
As well as being diagnosed with ADHD, Lewis has a number of ‘mental difficulties’, his barrister said.
‘His mental age is low and his cognitive skills are very poor,’ Mr Riordan told the court.
He added that psychiatric reports reveal the defendant has an IQ in the region of 55 or 56 and a mental age of nine or 10.
‘The time may come, and one hopes it will, when he may face the enormity of what happened. But that time is not yet with us.’
He is also considered ‘alcohol dependent’ and ‘shows evidence of harmful use of cannabis’, the court heard.
One of Miss Windsor’s relatives walked out of court as Mr Riordan said Lewis offered them his ‘sincere condolences’.
Outside the court Hannah’s mother, Gaynor Murray, burst into tears and said her family “could now find peace’.
She said: ‘He deserved what he got and I’m so made up.
‘It’s the best day of my life now we can finally mourn in peace for Hannah.
‘She was lovely, the smile on her face was unbelievable and she always tried to help everyone – she was my baby.
‘I hate him, I never ever use that word but I hate him. It’s never going to bring my little girl back but I’ve got justice today.’
Det Insp Mark Tivendale said: ‘On behalf of Merseyside Police I would like to offer my sincere condolences to Hannah’s family.
‘They have shown great dignity throughout this investigation.
‘Hannah was in the prime of her life. She should have been looking forward to the rest of her life but that was taken from her by Adam Lewis.
‘The sentence today willl not bring Hannah back but I hope the conclusion of this case will bring some closure to Hannah’s family and friends.’