John Barrett had a history of mental health problems

John Barrett, 42, from Putney, south-east London, was found guilty at the Old Bailey of the manslaughter of former banker Denis Finnegan, 50.

Barrett, who is receiving treatment at Broadmoor secure hospital, had pleaded guilty to manslaughter on grounds of diminished responsibility.

He stabbed Mr Finnegan to death in Richmond Park in September last year.

Mr Finnegan was cycling in the park when he was approached by Barrett who was said to have ambushed him and then stabbed him several times in the back and chest before walking off.

Denis Finnegan was killed while cycling in Richmond Park

Judge Scott-Gall told Barrett: "This was a planned and unprovoked attack on a completely innocent member of the public, a family man who was a complete stranger to you chosen at random.

"You had forearmed yourself with a knife with a 12in blade which you had purchased the day before."

Prosecuting, Crispin Aylett, said: "Mr Finnegan asked him: 'What have I done', then Barrett walked away and wondered to himself whether he had killed the 50-year-old or not."

Judge Anthony Scott-Gall told Barrett he would have to serve at least 15 and a half years before being considered for release.

If his care had been better it is our submission that he would not have been out on the streets or in Richmond Park and he would not have been in a position to kill Mr Finnegan Defence barrister Merida Harford-Bell

Barrett had been given leave from Springfield Hospital, in Tooting, south London.

The court heard that three psychiatrists had all diagnosed Barrett as suffering from paranoid schizophrenia with auditory hallucinations.

Defending, Merida Harford-Bell said: "If his care had been better it is our submission that he would not have been out on the streets or in Richmond Park and he would not have been in a position to kill Mr Finnegan."

An independent inquiry has been launched into the details surrounding the case.

South West London and St George's Hospital NHS Trust, which runs Springfield, said an "investigatory process" had begun into the consultant who dealt with Barrett's case the day before he killed Mr Finnegan.

The Home Office has confirmed it had received last month's letter from Mr Finnegan's brother John, in which he said he was "disappointed" at the government's failure to respond to his concerns over the management of Barrett's care.

A spokeswoman said a reply would be sent "imminently".