THE father of the man accused of murdering retired solicitor Don Lock has said his son is “scrupulously honest”.

John Daley told jurors trying his 39-year-old son Matthew Daley for murder: “[He is] honest to a fault in so much as he finds it difficult to lie about some things quite honestly; that’s something I would say about him.”

Matthew Daley is accused of murdering Mr Lock, 79, on the side of the A24 near Findon on July 16 last year. He accepts knifing Mr Lock but denies murder, claiming diminished responsibility due to mental health problems and saying he felt threatened by Mr Lock.

The defendant has an established diagnosis of autism with episodes of psychosis, jurors have heard, while his defence says he has underlying paranoid schizophrenia that had not been recognised or treated.

Giving evidence at the second week of his son’s murder trial yesterday, Mr Daley said he had kept a diary about his son as his mental health deteriorated in early adulthood.

“It was clear that his life and life expectations were draining away,” he told jurors.

“I did not want to be in my eighties and thinking, what could I have done to support my son in this.

“So it was therapeutic for me and also useful for the health professionals.”

Mr Daley recalled how his son was a “quiet” and “respectful” child who never pushed to the front of the queue.

He left school after getting good exam results at 16 or 17, then went to Chichester College with a view to becoming an architect, finishing top of his class.

He went from there to Portsmouth University to study architecture, where his father remembered how he worried his parents by suddenly flying off to Argentina.

Mr Daley said: “He had got his cheque for his grant and was studying in the library one afternoon and he was looking at a book and he was interested in this building in Argentina.

“He decided he would like to go and see that building, so that day he just went back to his flat, picked up his passport, and flew out to Argentina.”

In 2005 Matthew went to live in a bedsit in Worthing, where his father said he used to complain about noise from the neighbours, later thought to be auditory hallucinations.

“At the time we just thought that he was making a fuss,” his father said, “but that was the first clear point of us knowing that things are not right and these voices are a problem.”

In 2008 his son damaged a bed and doors in his house, and Mr Daley tried to get help, first with a speech and language therapist.

“But it was always the case with him, if anyone was getting close to his head or his psyche then he disengages, so that was a failure,” he told jurors.

Matthew trained and then got a job as a lifeguard in Brighton, his father said, but: “The things is that he takes things very seriously. And trying to guard a swimming pool with children jumping round making lots of noise caused him lots of stress.

“Particularly on a couple of occasions where he had to rescue children. There were a couple of occasions where he had done that and had to get sent home from work because the whole thought of it was so frightening that he could not work for the rest of the day.”

He said his son used to comment about people talking about him, and had turned his fridge around to face the wall as he said it was causing him problems in the head.

Jurors have been told that the defendant's parents frequently asked doctors for their son to have the treatment he needed and sometimes to be sectioned.

The chief executive of the Sussex Partnership NHS Foundation Trust has apologised for failings in his care, the court heard.

The court has heard how Daley used to call police so often to complain about voices that they warned him he could be charged with wasting police time.

Daley denies murder. The trial continues.