A man has been locked up for life for killing a teenager by slashing her throat with a broken bottle.

Richard Mark Hanson, 21, above, admitted the manslaughter of Gemma Roberts, 18, on grounds of diminished responsibility when he appeared before Leeds Crown Court.

Prosecutor James Goss QC said Hanson, who had displayed psychotic behaviour since he was aged three, attacked Gemma, a total stranger to him, as he walked past her in Holme Street, Liversedge, last September.

Bleeding profusely, Gemma staggered into the car park of the Swan Hotel in Bradford Road where staff and customers desperately tried to save her life.

The court heard yesterday that Hanson, of Stubley Farm, Stubley Lane, Heckmondwike, had exhibited disturbed behaviour from the age of three but in the weeks before the killing his mental health had deteriorated.

He had heard voices and thought people were plotting against him and on the day of the killing he had gone to his GP with his mother for help.

Hanson pleaded not guilty to murder but admitted manslaughter on the grounds of diminished responsibility and was sentenced to life imprisonment.

The Recorder of Leeds, Judge Peter Collier QC, told him: "It may never be safe to take the risk of releasing you."

The judge told Hanson that the killing was random and meaningless. He added: "You are a very dangerous young man. Gemma Roberts was walking down the street. You randomly and brutally robbed her of her life. Not only did you cut short her life you devastated the lives of her family.

"Her death was the culmination of several weeks in which you were getting increasingly out of hand. Eventually, on September 21, you were threatening almost everyone who passed you on the street and attacked several with a broken bottle in your hand.

"At the time of the killing you were suffering from a long-standing severe personality disorder and that seriously impaired your responsibility for your actions."

Prosecutor James Goss, QC, said that at 7.45pm on September 21 last year Hanson killed Gemma by cutting her neck with a broken bottle as he walked past her in Holme Street, Liversedge.

Mr Goss said that in the days before the killing Hanson had been behaving in an increasingly bizarre and aggressive way and that evening he was effectively out of control, threatening and punching virtually everyone he encountered.

He had been drinking wine and cider with his then girlfriend. He walked into Holme Street with his girlfriend walking ahead. Gemma Roberts was walking towards him.

Mr Goss said: "As they passed each other the defendant, in an act of random and irrational violence, swung his arm backwards and out into her neck. He still had the upper part of the broken bottleneck in his hand. Nothing was said. Gemma Roberts carried on walking but in fact she was mortally wounded."

Hanson, who has an IQ of only 78, went to a nearby petrol station, discarding the broken bottle on the way, where he stole two packs of lager.

Gemma, of Liversedge, walked to the car park of The Swan Hotel in Bradford Road and called for help before collapsing. Customers and the landlord brought towels and tried to stem the bleeding.

She was taken to Dewsbury District Hospital but despite resuscitation attempts was pronounced dead. The cause of death was an incised wound to the neck which severed her jugular vein. Hanson later met his girlfriend again and they carried on drinking, chatting and kissing until 2am. He was arrested the next day.

In a victim impact statement Gemma's mother Mrs Tracey Roberts said her daughter had died senselessly. Before her death she was the happiest she had seen her. Her boyfriend Ryan Adamson felt guilty he had not been there to protect her.

Mr Goss said Hanson, who has a long criminal record which included house burglaries, aggravated vehicle taking, dangerous driving and robbery, said medical experts were agreed that at the time of the offence Hanson was showing clear psychotic symptoms and was untreatable and extremely dangerous.

Eric Elliott, QC, for Hanson, said that in June last year he had suffered a head injury in a road accident which seemed to have been "pivotal". He added: "To coin his own words, this defendant was a walking time bomb, ready to explode."