A mum-of-one was dramatically cleared of murder today after the Crown withdrew all the allegations against her.

Laura McMurdo, 30, was formally found not guilty of killing Claire Turnbull at the flat the accused shared with Aaron Donald in Blairhill, on October 5 last year.

She had denied being responsible for killing the 36-year old single mother and attempting to defeat the ends of justice by removing the murder weapon and hiding it in a holdall.

Although her clothes and shoes were stained with Claire’s blood, a forensic expert told a jury at the High Court in Livingston yesterday that she had not been in the same room as the victim when she was killed.

Donald, 28, has formally admitted that he killed Claire by repeatedly hitting her on the head with a claw hammer, smashing her skull and spattering the floor, walls and ceiling with blood and brain matter.

However, he denies murder and attempting to defeat the ends of justice and has lodged special defences claiming he was suffering from a mental disorder and diminished responsibility at the time of the killing.

The jury had earlier heard Donald, who had drunk a huge amount of alcohol that day, telling police under caution that he had “lost it” when he saw Claire making sexual advances to his girlfriend.

He described how he grabbed Claire by the throat and punched her twice on the face before grabbing the hammer and hitting her on the head a number of times.

As the prosecution case came to an end today, forensic physician Dr Pryanjith Perera, 56, gave evidence that Donald had been exhibiting no psychotic signs or symptoms when he examined him at Dunfermline police station the morning after Claire's death.

Asked if he was concerned in any way about the accused’s mental health the doctor replied: “No.”

Dr Elspeth Pike, 33, a forensic psychiatrist with the community forensic mental health team at NHS Fife, said she had assessed Donald’s state of mind twice.

The first time, shortly after he was detained for murder, she said she was unable to elicit any symptoms of mental illness.

She said he had been diagnosed with an “emotionally unstable personality disorder”.

She explained: “It was my impression that he may experience difficulties managing his impulses and may have limited sense of self identity which prevents him from taking responsibility for his feelings and actions.

“People with this disorder have a marked tendency to act impulsively without consideration of consequences.

"They have rapid emotional mood swings, struggle to plan ahead, have outbursts of intense anger which may often lead to violence or behavioural explosions. These may be easily triggered by impulsive actions or criticism.”

She told the jury Donald had admitted abusing a number of different drugs including heroin, cannabis, cocaine, ecstasy, MDMA, acid, and other psychoactive substances known as legal highs.

He also indicated he had used Spice, a psychoactive substance, while on remand and told her he’d attempt to use “anything he could get his hands on”.

Asked if the drugs appeared to have had an adverse effect on him, she replied: “Yes. Psychosis potentially.”

She added: “Mr Donald would have some difficulty regulating his emotions but it wouldn’t impair his ability to regulate his behaviour, recognising the wrongfulness of his actions.

“The extreme emotional experience would contribute to initial reaction of pushing someone away but it wouldn’t contribute to ongoing actions. He retained responsibility for his actions.

“I wouldn’t expect that the personality disorder would result in the behaviour described in the alleged offence.”

The final piece of evidence presented to the jury was a joint minute in which Donald’s counsel, Bert Kerrigan QC, agreed that his client had repeatedly struck the deceased on the head with the hammer and was responsible for her death.

Advocate depute Bernard Eblett told the court: “After careful consideration of the evidence, the Crown are withdrawing the libel in respect of charges one and two in relation to the second named accused, Laura McMurdo.”

Judge Lady Scott found her not guilty and told her she was at liberty but asked her to stay in the building because she may be asked to provide a statement.

Claire’s mum Heather held her head in both hands and sobbed loudly as McMurdo was exonerated.

As she left the courtroom she furiously said to McMurdo’s mother: “I hope you’re proud of your daughter!”

The trial continues with professional witnesses for the defence expected to give evidence on Monday.