A knife-obsessed loner who stabbed schoolgirl Claire Tiltman to death in a "frenzied, rapid and brazen" attack in Greenhithe almost 22 years ago has been jailed for life.

He must serve a minimum of 21 years behind bars for the brutal, premeditated killing, which he carried out because of the "feeling of power" it gave him.

Former milkman Colin Ash-Smith, who was branded “a pure evil predator” by police, refused to be in the dock to hear Mr Justice Sweeney deliver the sentence.

Passing sentence, Mr Justice Sweeney said: "You not only ended Claire's young life, which was so full of promise, but also caused unbearable grief and upset to her family and friends."

In deciding Ash-Smith's minimum term before he is considered for parole, the judge had to sentence according to the law in 1993.

Had he committed the murder after a change in law in 2003, Mr Justice Sweeney said the minimum term would have been 30 years.

He added that Ash-Smith's previous convictions were aggravating features, and that there were no mitigating factors.

Although Ash-Smith refused to be in the courtroom itself he was in the court cells having been brought there from Belmarsh Prison.

Mr Justice Sweeney said he "only had himself to blame" for not owning up to Claire's murder when he was arrested in 1995.

At the end of his sentencing remarks the judge commended not only the Kent and Essex Serious Crime Directorate but also Claire's family and friends for their dignity throughout the trial and to "express his sorrow for the burden they had had to bear" for many years.

The 46-year-old, who once wrote he would “kill a schoolgirl” because, he claimed, it sounded “impressive”, has already spent 19 years in jail for two other near-fatal knife attacks on women, but denied murdering the 16-year-old in a dark alleyway off London Road in January 1993.

However, after a five-week trial at Inner London Crown Court, the jury of seven men and five women took just three-and-a-half hours to convict him unanimously.

He showed no emotion as the verdict was announced yesterday, and then refused to return to the dock after a short adjournment to hear impact statements made by family and friends read out to the court.

Sadly, Claire's parents Lin and Cliff died without ever seeing justice for their only child.

But Claire's friends from childhood and schooldays at Dartford Girls’ Grammar were in court on their behalf, having sat through every day of the compelling trial.

The hunt for Claire’s killer was one of the biggest murder investigations in Kent Police’s history.

Ash-Smith was first quizzed as a suspect after he was arrested for a knife attack on a 21-year-old woman in October 1995 and less than 400m from where Claire was savagely stabbed to death.

But at the time there was no evidence to link him to her murder.

However, a cold case review by police and a change in the law which enabled juries to hear a defendant’s “bad character”, including previous convictions and behaviour, were two of the crucial factors which led to him being charged in February this year and on the day Ash-Smith was due before the parole board.

This meant the jury were allowed to hear the horrific details of the 1995 stabbing of healthcare assistant Charlotte Barnard, and also how seven years earlier he had left a 27-year-old woman for dead in a Swanscombe quarry.

At gun and knifepoint she had been forced to strip, tied up and her mouth stuffed with tissues before Ash-Smith tried to rape her and strangle her with his old school tie. When it ripped in two he stabbed her five times in the back.

Ash-Smith was linked to that attack when half of the tie was found in his car by police after his arrest in 1995.

He later admitted attempted murder, attempted rape and kidnap in relation to his first victim, who cannot be identified for legal reasons, and causing grievous bodily harm with intent to Miss Barnard. He was jailed for life in December 1996, with a minimum term of 15 years.

The sentencing judge at the time told Ash-Smith his “aggressive and sadistic” fantasies meant he was “far too dangerous to be at large”.

The jury in the latest trial also heard from Ash-Smith himself when he gave evidence that he:

• Had a collection of 20 to 30 knives, including commando, sheath and flick knives;
• Wrote “assault plans” in which he described the 1988 attack as his “masterpiece” and rated it “95% successful”;
• In the same hand-written notes described other planned and aborted attacks, including the stalking of a woman at Swanscombe train station;
• Was obsessed with an ex-work colleague’s wife and broke into her home armed with a knife and planned to sexually assault her;
• Exploded in “anger and frustration” when he repeatedly stabbed Miss Barnard because he wrongly believed his fiancée was having an affair;
• Described himself as “an animal” and would go on “night walks” armed with knives and hoping to attack people;
• Had a “very limited moral compass” and a “darker side” to his personality.

The court also heard that he boasted about being dubbed the “Swanscombe Psycho” by friends and that shortly after Claire’s murder he pretended to attack his girlfriend in the street “to see if anyone noticed”.

Another important factor in the Crown Prosecution Service’s decision to charge Ash-Smith was a confession about Claire’s murder which he made while in HMP Wakefield between 2001 and 2003.

Ash-Smith told convicted sex offender Stefan Dubois he had seen someone on a zebra crossing and then "snapped and attacked".

The court was told that the conversation could only relate to Claire's murder as there was no crossing in the areas of either the 1988 or 1995 attacks.

"You not only ended Claire's young life, which was so full of promise, but also caused unbearable grief and upset to her family and friends..." - Mr Justice Sweeney

Claire, who was an only child, had left her home in Woodward Terrace, Horns Cross, at about 6pm on Monday, January 18, 1993, to walk less than a mile to a friend’s home in Riverview Road, Greenhithe.

However, Ash-Smith “intercepted” the teenager just before 6.30pm after she took a detour to buy cigarettes from a shop off Knockhall Chase before walking back down London Road.

Claire, who had celebrated her birthday just four days earlier, suffered nine wounds, some measuring up to 15cm deep, to her body before she managed to escape her attacker.

But she collapsed and died on the pavement despite desperate attempts by passers-by to save her life.

The court heard at the start of Ash-Smith's trial that the killing was carried out by a "ruthless, predatory, armed killer".

Prosecutor Brian Altman QC said Ash-Smith, who was 24 at the time and living with his parents in Milton Street, Swanscombe, attacked Claire "rapidly and stealthily", giving her no time to defend herself. There was no sexual motive or apparent robbery.

"This was a killing for the sake of killing," said the prosecutor.

Several witnesses claimed to have seen a man in a light-coloured, waist-length jacket walking down London Road at the time.

Ash-Smith was known to have "habitually worn" a similar jacket, and wore it to Claire's funeral just a few weeks later.

The jacket was examined by police after his arrest in 1995 but no forensic evidence linking him to Claire could be found.

It was later returned to Ash-Smith’s parents, former Labour councillors Diane and Aubrey Ash-Smith, but when police searched all known family addresses last year as part of their cold case review the jacket could not be found.

However, they did find a single newspaper cutting marking the first anniversary of Claire’s murder and a fresh appeal for her killer to be caught.

The court heard Ash-Smith phoned the police incident room the day after Claire's murder because he feared either he or his distinctive Ford Capri had been spotted that night.

But he made a “fundamental mistake”, said the prosecution, of putting himself in the area at the time Claire was murdered and therefore created a fake alibi when questioned by police six days later.

He claimed he had driven his mum to see a constituent before they returned home by 6pm, and remained there for the rest of the night.

However, Mrs Ash-Smith was not called by the defence to give evidence.

Mr Altman said: "Claire was a target for a completely senseless slaughter of an innocent, young, teenage girl, you might think for no better reason than the warped pleasure he derived from attacking a lone woman and the ultimate power and control it gave him."

The victim impact statements read in court were made by Cliff’s brother Roger, on behalf of the family, and by Lisa Gribbin, on behalf of Claire’s friends.

Both spoke of the devastating effect of her murder. Mr Tiltman said all Cliff and Lin’s “hopes and dreams” disappeared the night their daughter was killed.

He said the couple had always been over-protective of Claire but felt that having turned 16 just four days earlier, she should have more freedom.

However, Mr Tiltman said that decision caused "massive amounts of guilt".

He added that he believed Claire's death and the resulting stress led to the couple's early deaths.

Lin was just 56 when she died in 2008 from cancer of the oesophagus and Cliff developed five inoperable tumours before dying at the age of 62 in 2012.

Roger Tiltman, who was not in court, added in his statement: "It is very sad that Cliff and Lin could not be in court today to see the person who killed Claire has finally been brought to justice."

Mrs Gribbin, who was one of the seven friends who set up the Justice for Claire campaign, wrote of the "beautiful and loyal" best friend with a "wicked sense of humour".

She and Claire were both doing their Duke of Edinburgh Award at Dartford fire station when she was murdered.

"When I went back (to school) all of her friends would just stare at Claire's empty chair," she wrote. "We were just devastated."

Tragedy even continued during the trial when Lin's cousin, Len Rumbul, suffered a stroke in court. He is still in hospital recovering.