A jury has retired to consider its verdict in the trial of a man accused of the "road rage" murder of a retired solicitor following a minor shunt.

Matthew Daley, 35, knifed 79-year-old Donald Lock 39 times on the A24 at Findon, near Worthing, West Sussex, on July 16 last year, jurors heard.

The trial was told Daley stabbed Mr Lock after his Toyota crashed into the back of Daley's Ford Fusion at about 16mph, causing minor damage to both cars.

The crash happened after great-grandfather Mr Lock, who was returning from a cycling meeting, was forced to brake after Daley made an emergency stop.

After a "calm" Mr Lock got out of his car to ask why he had braked so suddenly, Daley knifed him, while remaining calm "like Jesus Christ", jurors heard.

Daley attacked him with a four-and-a-half inch knife. A witness heard Mr Lock yell: "Help, help, get off me."

Another witness said Daley, who is being held in Hellingly medium-secure unit in East Sussex, looked "expressionless" during the attack, like he was "having a passport photo" taken.

Brighton and Hove Albion season ticket holder Mr Lock, who had recently been given the all-clear from prostate cancer, died at the scene. The cause of death was a stab wound to the aorta.

The trial, at Lewes Crown Court in front of Mr Justice Singh, heard Daley had suffered mental health problems for 10 years, and his family had "pleaded" with experts to section him.

His mother Lynda Daley told jurors he was never given a proper diagnosis, that they had not been listened to by health professionals and that they often lived in a state of anxiety.

And his father John Daley broke down as he said the killing need not have happened if his son's mental health had been treated "properly".

Daley's mental health decline stemmed from the breakdown of his parents' marriage while he was studying architecture at the University of Portsmouth, jurors were told.

A week before the trial, the chief executive of Sussex Partnership NHS Foundation Trust apologised to Daley's family, saying their care of him "should have been better", the trial heard.

Of the apology, Mrs Daley said: "It's 10 years too late."

She went on to disclose how Daley confessed to the killing just as she was about to enter a police station, amid fears he may be involved following media reports about Mr Lock's death.

Following the stabbing, Daley parked his car at Woodland Stables in Patching where he helped out. He was arrested the following day near Worthing golf course with a blood-stained knife in his bag.

Daley did not give evidence at the trial. In a videoed police interview he described feeling "threatened and afraid" as he claimed Mr Lock tailgated him while seeing him allegedly shouting obscenities in his rear view mirror.

He told officers: "I just saw someone very close and very angry and I wanted that scenario to stop because it was intrusive."

Expressing sorrow, Daley added: "I'm not happy that the man has died. I'm not happy that in the final minutes of his life he was in that much pain, and I don't want to be reminded of it.

"I feel very sorry about what I have done and I don't want to see anything like that happen in my lifetime again."

Forensic psychiatrist Dr Roderick Ley said he believed Daley had been wrongly diagnosed with Asperger's and had an underlying paranoid schizophrenic illness that was undiagnosed for years.

Another expert, consultant forensic psychiatrist Dr Philip Joseph, said Daley was not psychotic at the time of the killing, pointing to the absence of audio hallucinations as an example.

Listening to the evidence throughout the trial has been Mr Lock's wife of 55 years, Maureen, and their son Andrew, alongside Daley's parents.

Daley, formerly of St Elmo Road, Worthing, denies murder.

The jury was sent home for the weekend and will resume its deliberations from 10.30am on Monday.