The mother of tragic Sarah Lawson said she too could have killed her daughter to end her torment.

Karen Lawson, 45, said she understood why her husband Jim had fed their 22-year-old daughter a cocktail of drugs before holding a pillow over her face until she stopped breathing.

She said: "We had both reached the point when we could not cope any longer.

"It could easily have been me who killed Sarah. On another day, if circumstances had conspired in such a way, it certainly would have been."

Mrs Lawson was in bed in the family's home in Georgia Avenue, Worthing, when her daughter died in a nearby room.

At 4am her husband called the police to say he had killed her and within five minutes, officers and paramedics were in the house.

Their efforts to revive Sarah failed and when Mrs Lawson saw her daughter she collapsed.

She said: "I went downstairs and hugged Jim and he told me what he had done. We were living with this person who we knew would kill herself eventually. It was just a case of waiting for it and the stress was almost unbearable."

Since the death of her daughter in April 2000, Mrs Lawson, who has a 21-year-old son Jamie, has separated from her husband but still supports him.

She said: "I could not stay in the house any longer.

"There were too many bad memories and I could not cope with being there. This has ripped my family apart.

"Jim is a very gentle, honest, caring man. He is mortified to think people may think he is malicious. That isn't true. He just loved his daughter."

Trevor Pettifer, a family friend and Lawson's boss, said Lawson, a roofer, had originally denied murdering his daughter because he had wanted the torment she and his family had suffered to be made public.

He said: "He had decided to turn down pleading guilty to manslaughter on the grounds of diminished responsibility because he thought there would have been no interest in it.

"He was prepared to sacrifice five or seven years of his freedom to try to show the devastation caused by mental illness."

Sarah Lawson's mental health problems began a few years after she started Davison CE Girls' High School in Worthing.

Her mother said she was an average student who had good friends. She stayed on to pass her GCSEs before going on to Northbrook College to study social work.

But she only completed the first year of her course after her mental state gradually deteriorated.

Years of cutting herself had left deep wounds on her arms, which eventually required cosmetic surgery.

Mrs Lawson said: "At first we thought it was adolescence but it wasn't long before we realised something was seriously wrong.

"She walked around holding her pyjama sleeves down over her arms because she was embarrassed about cutting herself . We didn't know what was happening.

"I eventually discovered razor blades in her bedroom and bandages caked in blood."

Throughout her teens, Sarah regularly visited her GP and mental health workers but as she got older her bouts of depression worsened.

She empathised with Richey Edwards, the guitarist with the rock band Manic Street Preachers who is believed to have committed suicide by jumping from a bridge. His body was never found.

Mrs Lawson said: "She was in a record shop in Brighton and saw a picture showing he had cut his arms too. It was like there was someone else out there suffering like her."

Eventually, Sarah began attempting to take her own life.

Mrs Lawson said: "She was prescribed lithium and so many other drugs she had to wear a medic alert disc around her neck in case anything happened to her.

"She was regularly taking overdoses but it was just a case of her having her stomach pumped and then being sent home. Nothing was ever done to try to stop it happening in the first place."

Mrs Lawson said her daughter turned to alcohol to try to cope.

She said: "Sarah did anything she could to try to numb the pain and drink was a way of doing that.

"She was addicted to prescribed drugs but there has never been any indication she used cannabis or any other recreational drug."

Mrs Lawson said the family ended up in a cycle of torment with Sarah suffering bouts of intense depression with occasional periods of happiness.

She spent hours under her duvet unable to come out of her room.

She said: "She was a bright, good-looking girl who knew what was happening to her and it was destroying her.

"She just did not want to be alive because the suffering was too much."

Weeks before her death, Mrs Lawson thought her daughter had finally got over her illness and the family could put the decade of pain they had endured behind them.

In March 2000 ,Sarah went to America for a holiday to stay with a friend she had met over the internet.

Her mother said: "We chatted about going to see the Manic Street Preachers in concert and planned a trip to Glastonbury together.

"It was like we had got our old Sarah back who was into her music and had lots of friends."

But the happiness did not last and within weeks Sarah plunged into another bout of depression.

Days later she was dead.

Mrs Lawson said: "I found her dressing gown belt with tight knots in it. I asked her if she had tried to kill herself but she went quiet. She later told her dad she had tried to hang herself. No one seemed to want to help us."

As soon as he heard about her death, Sarah's distraught boyfriend David Ripley threatened to kill himself if he was not admitted to Homefield Hospital.

Mrs Lawson said: "So many people have suffered. Lessons have to be learnt from what happened with Sarah.

"In a way she was lucky because she had her family and their support around her, which others do not, but she was mentally ill and needed help.

"Thousands of people must be going through a similar ordeal. Something must be done to change it."

Marjorie Wallace, chief executive of mental health charity Sane, said Miss Lawson's death was a tragedy that should not have happened.

"This case echoes many of the thousand calls a week we receive from individuals enduring the torments of mental pain who are being turned away, and families driven to the flashpoint of despair.

"One in seven people with serious mental illness will take their own life.

"People like Sarah, if given constant care, time and space, and their families given support, can respond to treatment.

"No one should be turned away from hospital or left to feel as angry and hopeless as Sarah did in the face of the services that did not help her."