A 17 year old boy with a fixation on a TV serial killer has been sentenced to a minimum of 25 years in prison for killing and dismembering his girlfriend.

Steven Miles, then 16 and of Surrey, killed 17 year old Elizabeth Thomas at his family home on January 24. Miles stabbed Thomas several times, killing her, before he dismembered her legs and arm, and placed her body parts in bin bags.

Miles used his father’s tools – from a tree surgery business – to cut Thomas’s body.

The teenage student had previously been diagnosed with a form of autistic syndrome and had been referred to his GP and mental health services after he began to self harm in 2012. Miles told his family a voice in his head – who Miles called Ed – told him to kill a person.

Miles was fascinated by American TV show Dexter, which tells the story of a police officer who is simultaneously a serial killer.

When Miles’ sister came home to the family flat her brother told her “Ed made me do something bad.”

In October 2013 Miles was discharged by mental health services who adjudged the teenager to be making good progress following a period out of school due to his condition.

Judge Christopher Critchlow said psychiatrists had agreed Miles did not suffer from schizophrenia and was therefore could not claim diminished responsibility.

Miles was sentenced to a minimum term of 25 years. The judge admitted he would have preferred a whole life term, but as Miles was a child he was unable to do that. Miles showed no emotion when the sentenced was passed.

Critchlow warned at the start of the trial that the details were “extremely unpleasant.” said: "This is a case of the utmost gravity, the horrific features of which are rarely heard in any court.

"Nothing this court can say or do, no sentence this court can impose can alleviate the pain suffered by Elizabeth Thomas' family for death in such a terrible manner. There must be a life sentence,” he added.

The Thomas family described Elizabeth as a "kind, caring, loving and gentle girl.”

Lewis Power QC, defending Miles, said the killing was inspired by TV show Dexter, of which Miles was an obsessive fan.

Power said: "He had pleaded guilty to a horrendous crime which is beyond belief because of its horrific nature.

"This was a truly gruesome killing ripped from the pages of a hit TV script. The evidence points to the defendant trying to emulate the actions of the character Dexter who he idolised.

"The case is a sad testament to the perils of how young people can become entrenched in modern TV blockbusters involving violence which shockingly led to a copy-cat killing in real life," Power added.