A Newcastle man serving life for the "ferocious" knife murder of a 12-year-old girl in her own bedroom must serve at least 13 years behind bars before being considered for parole, a top judge ruled today.

Ronald Pattinson was just 18 when he was convicted of Natalie Ruddick's murder at Newcastle Crown Court in October 2003. He stabbed Natalie 25 times in the bedroom of her Newcastle home on March 5 2003 in a crime which shocked the city.

Today at London's Royal Courts of Justice, Mr Justice Andrew Smith, who presided over Pattinson's trial, fixed the minimum "tariff" he must serve for his crime at 13 years, less the 234 days he spent on remand pending his trial.

That means it will be 2016, when Pattinson will be aged in his 30s, before he can apply to the Parole Board for release. Even then he will only be freed if he is no longer considered a public danger and, for the rest of his life, will remain on "life licence", subject to recall to prison if he puts a foot wrong.

In reaching his decision today, Mr Justice Smith said he had "read carefully" letters from Natalie's parents, but also took into account that Pattinson had only just turned 18 at the time of the killing.

He was also of "significantly low intellect" and, although the motives for the murder remained unclear, the judge accepted the killing "was not planned or premeditated".

The judge said Natalie the 25 stab wounds had been inflicted with a small knife, the kneck wounds proving fatal. There were defence wounds on her right arm and she had also been asphyxiated, either by being held in an arm lock or being smothered with something soft.

The youngster had been off school due to sickness for some days and was alone in the house when Pattinson killed her.

"Her parents sold contraband cigarettes from their house, and Natalie, who enjoyed selling them for her parents, collected at least £30 from cigarette sales during the morning, putting the money in a plastic tub in the living room. "Natalie was discovered by her 15-year-oold sister Emma when she returned from school...and went into the house with another sister, Claired, aged 16, and their mother.

"In response to Emma's screams, Claire went to Natalie's bedroom and courageously attempted mouth-to-mouth resuscitation, but Natalie was already dead."

The judge said Pattinson was Claire's boyfriend and had smoked cannabis shortly before entering the Ruddick home to find Natalie at home alone.

It was the prosecution's case at trial that Natalie had seen him stealing the cigarette money and, in order to cover up the theft, he chased Natalie to her bedroom and killed her.

Although there was "some basis for this hypothesis", the judge said it would be wrong to speculate on Pattinson's motives and there was no reason to think the killing was planned or that it was "a murder for gain".

The judge added: "Ronald Pattinson must have attacked Natalie ferociously to inflict the injuries that he did. The offence was aggravated because she was aged only 12 years and was therefore vulnerable.

"I also observe that she was killed in her own home, where she was likely to be, and was in fact, discovered by her own teenage sisters."

But, "despite the aggravating features", the judge said Pattinson's tariff should be fixed at 13 years and he should be given credit for the 234 days he spent on remand before his trial.