The father of a man accused of the "road rage" murder of a retired solicitor broke down in court as he said the killing need not have happened if his son's mental health had been treated "properly".
John Daley told Lewes Crown Court that his son, Matthew Daley, who is on trial for allegedly murdering Donald Lock, would regularly "hear voices" causing him to attack people in the street.
He told the court that he had written repeatedly to his son's mental health team warning them that his son "could hurt someone or worse" and there could be a "fatality".
Mr Daley said: "There has been no let up in these symptoms, I witnessed them on a daily basis."
He described how the 35-year-old became increasingly jealous about his girlfriend, Lea, and would assault people after he heard voices saying that she had been sleeping with other men.
Mr Daley said: "He would get involved in altercations with people in the street, he would attack people, he would grab them round the neck, held them down and generally got into a fight."
The court has heard that Daley had been suffering from mental health problems for 10 years, and his family had "pleaded" with mental health experts to section him.
Earlier, the court heard from an expert who said he believed Daley had been wrongly diagnosed with Asperger's and had an underlying paranoid schizophrenic illness that was undiagnosed for years.
Mr Daley described how he was in France on holiday when Mr Lock was killed and he read reports about the incident on the internet.
He said he realised immediately his son was involved and he called his daughter and asked her to help the police detain Daley.
He said: "My heart sunk in my boots and I thought 'My god, it's come to pass'."
Breaking down, Mr Daley continued: "All our nightmares had come to pass and just unnecessarily because I know that people with mental conditions like this can be treated, people can be sectioned, people can have injections and these things do not need to happen.
"I am thinking to myself, this poor man and his family will have to live with my son's actions for the rest of their lives.
"They will never be able to understand what happened, their lives have been ruined, my son's life and expectations have been ruined and it didn't have to happen.
"Had I been more assertive and angry in my dealings it might not have happened. I have always had a measured response with the authorities - it's not the way to deal when you have a problem, you must shout and scream from the rooftops because being reasonable never gets an outcome."
Mr Lock, 79, was knifed 39 times after crashing at about 16mph into the back of Daley's Ford Fusion car on the A24 at Findon, near Worthing, West Sussex, last July 16.
The minor crash happened after great-grandfather Mr Lock, who was returning from a cycling meeting, was forced to brake suddenly after Daley made an emergency stop.
Brighton and Hove Albion season ticket holder Mr Lock, who had recently been given the all-clear from prostate cancer, died at the scene as Daley sped off.
Daley, formerly of St Elmo Road, Worthing, denies murder.
In an earlier incident, in June 2012, while Mr Daley was previously also on holiday in France, his son smashed the windscreen of a car belonging to a family friend before standing "menacingly" with the hammer on his doorstep.
He told the court that his son's anxiety levels rose when he or Daley's mother were away.
Mr Daley said: "He picks up a hammer, walks all the way to the friend's house and smashes the windscreen of this friend's car.
"He then stands menacingly with the hammer in his hand, my good friend opens the door to be greeted with Matthew standing there with the hammer."
He said he cut his holiday short to ask for intervention from his son's mental health care team, but was told he could not be sectioned "unless he hurts someone".
He said he attended a meeting with his son's psychiatrist and was told Daley had agreed to take his medication.
Mr Daley said he requested further help but was told because the police had not considered the hammer incident as "important", it did not warrant a crisis team supervising his medication.
He said a crisis team was allocated, but added: "Here's the killer blow - then the crisis team staff wouldn't enter Matthew's flat because he had this issue with the hammer.
"I am absolutely gob-smacked, I am absolutely in trauma. I am incensed because this is absolutely crazy."
Mr Daley said that his son was a "clever" and "gentle" man who would give the psychiatrists the "right answers" because he did not want to suffer the stigma of being labelled as suffering from a mental illness.
He said this led to him being repeatedly diagnosed as showing no psychotic symptoms.
The court heard that in September 2013, Mr Daley wrote a letter to his son's doctor, saying: "I am concerned Matthew could end up hurting someone or worse unless he resumes taking his medication."
He then wrote a further letter in March 2014, saying: "It would appear you are not treating him properly as he is still carrying out unprovoked attacks on people in the street, most recently on Friday in Broadwater (Worthing) where police were involved.
"I am worried that it will end up with a fatality unless Matthew gets help with his obsessional behaviour and the voices."
The court was told that the defendant's girlfriend had also written expressing her similar concerns.
Mr Daley added: "I am sure that he is not getting treated properly. I do not know about the diagnosis because I am a lay person, to me the diagnosis means nothing.
"He is severely ill and needs looking after."
Mr Daley said his son's obsessional behaviour, as well as confronting strangers in the street and following someone home from the gym, included running for three hours a day, and at one point the animal-lover attempted to purchase several horses which he had no means to look after.
Daley, who has no previous convictions, had also acted violently towards his partner in the days before Mr Lock's death, the court heard.
The trial continues.