Mackay attacked his victim in the street

Ron Mackay was originally charged with the murder, however, at the High Court in Edinburgh the Crown accepted his guilty plea to the culpable homicide of George Williamson.

The court was told Mackay, 35, a former part-time soldier, of Monksbarn Gardens, Edinburgh, had punched his victim and thrown him to the ground on 24 June last year.

Lord Philip told the jury it had been a "distressing and tragic case" and deferred sentence for background reports.

Mental illness

Mackay had served in the Territorial Army but was discharged in 1988 because of mental illness and diagnosed as a paranoid schizophrenic the same year.

Three days after attacking Mr Williamson, a retired solicitor, Mackay handed himself into the Royal Edinburgh psychiatric hospital.

The court heard that the attack was witnessed by a team distributing leaflets for a supermarket.

Advocate depute Geoffrey Mitchell QC told the court that Mr Williamson, of Park Gardens, Edinburgh, possessed his "full mental faculties".

"Although frail he was a relatively fit man for his age," Mr Mitchell said.

Nothing I can say should detract from the tragedy of the death of Mr Williamson David Burns QC

Mackay's counsel David Burns QC said his client had been under various forms of medication for several years.

"His offending is connected with his illness and from his records one can see that round about the time of his offending there are admissions to hospital voluntarily," he said.

Mr Burns said Mackay remembered being at the pub on the day of the attack.

Mackay believed he went to his brother's house and took some of his tablets.

Blood clot

Eyewitnesses said they saw Mackay staggering and Mr Burns said this may have been caused by his medication.

Mr Burns added: "Nothing I can say should detract from the tragedy of the death of Mr Williamson."

Mr Williamson was helped home after the attack and later taken to Edinburgh Royal Infirmary.

He had suffered a cut right hand and grazed arm.

Mackay is being assessed by doctors

But later that evening his wife noticed he appeared confused and he was re-admitted to hospital.

A scan revealed a blood clot between the skull and the surface of the brain.

Lord Philip ordered that Mackay, who has been held at Carstairs State Hospital, should be assessed by doctors.