A youth who sadistically tortured and mutilated his 17-year-old girlfriend before strangling her and burying her in a shallow grave was put behind bars for life.

A judge told 18-year-old Adam Lewis, "That was a prolonged, merciless and terrible attack which must have been agonisingly painful for Hannah Windsor before she died."

Liverpool Crown Court heard that he had tied Hannah to a tree at a Wirral beauty spot and covered her mouth with sticky tape, brutally assaulted her and mutilated her with a Swiss army knife.

"Only you know exactly 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," said Mr Justice Holroyde.

He ordered Lewis must serve a minimum of 22 years.

He told Lewis, who has a low IQ, the mental age of about nine and behaviour disorders, "I am quite sure that your murder of Hannah Windsor involved both a sexual and a sadistic element."

Detailing Hannah's ordeal the judge said that the evidence of the very experienced pathologist "makes chilling reading."

The judge said that he had also gouged deeply into the thigh with the knife, strangled her with a length of nylon cord which he had found nearby and may also have manually throttled her.

Lewis, who had been camping out on Bidston Hill while on the run from police for breaking into the home of his sister's ex-partner and setting fire to it, then moved her body about 25 metres and buried her in the woodland.

Liverpool Crown Court heard that in the view of the pathologist the nature and extent of the injuries Hannah "had been the victim of torture".

Lewis, of Fairmead Road, Moreton, had been due to stand trial on Monday accused of murdering and raping her but he changed his plea to guilty to some of the charges he faced.

He pleaded guilty to murder, two charges of assault by penetration, burglary, and arson. He denied two charges of rape.

Neil Flewitt, QC, prosecuting, told the courtroom, crowded with friends and relatives of Hannah, that at the time of her death in May this year she had been living in a hostel for young homeless adults on Old Chester Road, BIrkenhead after difficulties in her life.

Lewis, who was living with his grandparents, knew her as they had gone to the same school and had similar difficulties and had been going out together for ten months.

He had set up camp near BIdston Observatory on Monday, May 14. That afternoon Hannah told a health engagement worker that he had set fire to his sister's flat and killed her baby and she was going to tell the police as he was "not a nice person."

The worker warned her not to see him alone and that evening the police came to her mum's home where she had gone and she told him where he was camping and said he had a gun. "She told him he had threatened to shoot any officer who came near to him."

The next day she was spoken to by police, who were concerned that he had a gun, on three occasions and she said she was giving information as her "civic duty". She asked if she should meet him and was told not to do so and was given a piece of paper with the telephone number for BIrkenhead CID in case he contacted her.

Mr Flewitt said, "Following the later discovery of her body some torn pieces of that note were found near to his campsite. It may be that the presence of that torn note around the campsite indicated that she had been speaking to the police and may in part explain why he attacked and killed her."

On Friday her mum realised she was missing and informed the police. At 9am that morning police at Bidston railway station on unrelated matters found Lewis sleeping beneath the foot bridge.

He was arrested for the burglary and arson and when searched was discovered to have the BB gun on him. He was taken to the police station and interviewed about those offences and then released.

Lewis spoke to his sister and said, "I've done something really bad. I have killed someone." Questioned he said it was Hannah but then said he was joking and she did not know whether to believe him.

He was taken to Bidston Hill and he took them to the burial site.

The pathologist who carried out the post mortem examination found she had been asphyxiated by the tape over her mouth and strangulation. There were ligature marks but he could also have manually strangled her.

When interviewed he gave a prepared statement saying that she had struck him and he strangled her with a piece of nylon rope he was playing with at the time, buried her and covered her up.

Questioned he denied losing his self-control after finding the piece of paper.

Stephen Riordan QC, defending, said Lewis had been known to child and adult mental health services since the age of seven.

Lewis was described as having been severely neglected at home which was why he was moved to the home of his grandparents.

“Although he was thought to be at risk of harming another human being nobody was able to predict what happened," said Mr Riordan.

He suffers a number of problems including attention deficit hyperactivity disorder (ADHD), mild mental retardation and poor cognitive skills.

He has a low IQ, the mental age of a nine or ten year old, suffers from an emotionally unstable personality disorder, and was dependent on alcohol.

He also suffers from dis-social personality disorder meaning he is ‘unconcerned with the feeling of others’ and has a low frustration tolerance.

However despite his mental disorders two independent psychiatrists agreed they were not the ‘driving force’ behind his killing of Hannah.

Speaking outside court, Hannah's mother, Gaynor Murray, broke down in tears as she said: "He deserved what he got and I'm so made up.

"Today was the best thing that could have happened - now we can actually mourn in peace for Hannah, my beautiful little girl."

Mrs Murray described her daughter as "lovely".

She said: "The smile on her face was just unbelievable. She was always trying to help everyone, she was a lovely little girl - she was my baby."

Asked for her thoughts on Lewis, Mrs Murray said: "I hate him for what he's done.

"It's not going to bring my little girl back but I've got justice today and I'm happy."

Hannah's emotional father, Paul Windsor, said: "I'm made up with the sentence today.

"From what I have been told, he will never get out - but if I got hold of him..."

Mr Windsor said of his daughter: "She was a beautiful girl."

Detective Inspector Mark Tivendale, of Birkenhead CID, said: "Hannah was in the prime of her life and she should have been looking forward to the rest of her life but sadly her future was taken from her by Adam Lewis.

"The sentence today will not bring Hannah back but hopefully the conclusion of this case will bring some closure for Hannah's family and friends."