Matthew Daley has been found guilty of manslaughter on the grounds of diminished responsibility following the "road rage" killing of a great-grandfather.
The 35-year-old was cleared of a charge of murder at Lewes Crown Court on Monday following the killing of Donald Lock, 79.
Lock was stabbed 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.
Before the killing Daley's family had "pleaded" with clinicians to section him as his mental health declined, the trial heard. NHS chiefs have apologised to his relatives for not doing more.
Daley sat emotionless in the dock flanked by two people.
Mr Justice Singh adjourned sentencing to July 8. Jurors were told how a "calm" Lock got out of his car to ask Daley why he had braked so suddenly.
Daley then launched a knife attack on him while remaining calm "like Jesus Christ".
As Daley stabbed with a four-and-a-half inch knife, he allegedly told Lock to "die, you f***ing c***".
A witness also heard 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.
Passer-by Andrew Slater tried to remonstrate with Daley, telling him: "Come on mate, leave it out."
But Slater retreated to his car when he saw a knife in Daley's clenched fist.
Brighton and Hove Albion season ticket holder 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 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 how they often lived in a state of anxiety.
Recalling the moment she realised her son was suspected of the killing, she said: "I couldn't believe it but, because of where it was, my heart sunk and all I kept thinking was 'We tried our best'."
His father John Daley broke down as he told how the killing need not have happened if his son's mental health had been treated "properly".
He said: "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."
One expert said when Daley first came to the attention of mental health teams, it was deemed he had schizophrenia, but that diagnosis was later revised to autism.
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".
Of the apology, Mrs Daley said: "It's 10 years too late."
She went on to reveal 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 Lock's death.
He told her: "I need to know where you are and that I can trust you."
He then said he had done "something really bad or something really wrong".
In a quiet voice, he went on: "I killed someone", before adding: "I want you to think about what I just said and ring me back in 10 minutes."
It emerged during the trial that the night before Lock's death, Daley paid a prostitute called Hannah between £60 and £80 for sex in Brighton.
In a videoed police interview, Daley spoke in detail about the moments leading up to the confrontation.
He described feeling "threatened and afraid" as he claimed Lock tailgated him while allegedly shouting obscenities from behind his wheel as Daley looked in his rear-view mirror.
Daley 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."
While on remand, Daley tried to send a letter to the BBC. In it, he offered a further account of what happened after the crash.
He wrote: "I didn't want to look at his angry face so I turned towards my driver's door and just put my feet onto the road.
"I could feel the other cars all stopping behind me. When I looked out of the door I could see him shouting and swearing.
"Because of my autism, the other sounds were silent. He walked fast up to me wearing bright colours. About a metre and a half away, I stood up, moving his aggression away from me.
Daley's younger sister, Rebecca Daley, described the death as "everything we feared would happen over the last 10 years".
His father recalled how he knew instantly his son was involved in Lock's death after reading news reports while he was on holiday in France.
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.
After the conviction, Colm Donaghy, chief executive of the Trust, said: "On behalf of the Trust, I apologise unreservedly because the care we provided to Matthew Daley should have been better.
"I also want to offer my sincere condolences to the family of Don Lock and everyone else affected by this tragic, devastating incident.
"Mr Daley was referred to our services in January 2008. He received treatment from our early intervention service, which helps people who are starting to experience the symptoms of psychosis.
"He was later transferred to the care of one of our community mental health teams where he received treatment for a combination of Asperger's syndrome (a form of autism) and psychosis.
"Having reviewed his care, it's clear that we should have reviewed Mr Daley's diagnosis, looked at other ways of providing treatment, done more to help him manage his symptoms of psychosis and listened to his family more closely.
"We got things wrong. But I do not believe that any of our staff acted in a way which was deliberately negligent or designed to cause harm. They knew Mr Daley well and believed they were doing the right things to help him. We will do things differently as a result of this tragic incident.
"The care and treatment we provided will now be subject to an independent inquiry commissioned by NHS England.
"In the meantime, we have commissioned our own independent review, jointly with NHS England, of all homicides from 2011 to 2016 involving patients known to Sussex Partnership NHS Foundation Trust.
"We have done this because we want the public, people who use our services and the organisations which commission them to be assured that we have done everything we should have in response to these tragic cases. We will publish this report in full."
Outside court, Lock's son Andrew - stood beside the pensioner's widow, Maureen - blamed the NHS for his father's death.
He told reporters: "As a consequence of the failings of the NHS and this verdict, it is clear that dad would still be here today if they had done their job properly."
He added: "It is upsetting to hear that the NHS have taken the trouble to write to the Daley family to apologise for their failings, yet we as a family have received nothing in writing ourselves."
Lock said his father was simply "in the wrong place at the wrong time".
And he added: "This verdict effectively provides the Daley family with what they have wanted for the last few years, their son in a safe place, away from harm's way, and being treated correctly.
"For them, they can still visit their son, hug him and talk to him and enjoy aspects of his life with him albeit constrained at the same time.
"For us, all we can do is cling on to the wonderful memories of dad."
His father John Daley broke down as he told how the killing need not have happened if his son's mental health had been treated "properly".
He said: "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."
One expert said when Daley first came to the attention of mental health teams, it was deemed he had schizophrenia, but that diagnosis was later revised to autism.
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".
Of the apology, Mrs Daley said: "It's 10 years too late."
She went on to reveal 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 Lock's death.
He told her: "I need to know where you are and that I can trust you."
He then said he had done "something really bad or something really wrong".
In a quiet voice, he went on: "I killed someone", before adding: "I want you to think about what I just said and ring me back in 10 minutes."
It emerged during the trial that the night before Lock's death, Daley paid a prostitute called Hannah between £60 and £80 for sex in Brighton.
In a videoed police interview, Daley spoke in detail about the moments leading up to the confrontation.
He described feeling "threatened and afraid" as he claimed Lock tailgated him while allegedly shouting obscenities from behind his wheel as Daley looked in his rear-view mirror.
Daley 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."
While on remand, Daley tried to send a letter to the BBC. In it, he offered a further account of what happened after the crash.
He wrote: "I didn't want to look at his angry face so I turned towards my driver's door and just put my feet onto the road.
"I could feel the other cars all stopping behind me. When I looked out of the door I could see him shouting and swearing.
"Because of my autism, the other sounds were silent. He walked fast up to me wearing bright colours. About a metre and a half away, I stood up, moving his aggression away from me.
Daley's younger sister, Rebecca Daley, described the death as "everything we feared would happen over the last 10 years".
His father recalled how he knew instantly his son was involved in Lock's death after reading news reports while he was on holiday in France.
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.
After the conviction, Colm Donaghy, chief executive of the Trust, said: "On behalf of the Trust, I apologise unreservedly because the care we provided to Matthew Daley should have been better.
"I also want to offer my sincere condolences to the family of Don Lock and everyone else affected by this tragic, devastating incident.
"Mr Daley was referred to our services in January 2008. He received treatment from our early intervention service, which helps people who are starting to experience the symptoms of psychosis.
"He was later transferred to the care of one of our community mental health teams where he received treatment for a combination of Asperger's syndrome (a form of autism) and psychosis.
"Having reviewed his care, it's clear that we should have reviewed Mr Daley's diagnosis, looked at other ways of providing treatment, done more to help him manage his symptoms of psychosis and listened to his family more closely.
"We got things wrong. But I do not believe that any of our staff acted in a way which was deliberately negligent or designed to cause harm. They knew Mr Daley well and believed they were doing the right things to help him. We will do things differently as a result of this tragic incident.
"The care and treatment we provided will now be subject to an independent inquiry commissioned by NHS England.
"In the meantime, we have commissioned our own independent review, jointly with NHS England, of all homicides from 2011 to 2016 involving patients known to Sussex Partnership NHS Foundation Trust.
"We have done this because we want the public, people who use our services and the organisations which commission them to be assured that we have done everything we should have in response to these tragic cases. We will publish this report in full."
Outside court, Lock's son Andrew - stood beside the pensioner's widow, Maureen - blamed the NHS for his father's death.
He told reporters: "As a consequence of the failings of the NHS and this verdict, it is clear that dad would still be here today if they had done their job properly."
He added: "It is upsetting to hear that the NHS have taken the trouble to write to the Daley family to apologise for their failings, yet we as a family have received nothing in writing ourselves."
Lock said his father was simply "in the wrong place at the wrong time".
And he added: "This verdict effectively provides the Daley family with what they have wanted for the last few years, their son in a safe place, away from harm's way, and being treated correctly.
"For them, they can still visit their son, hug him and talk to him and enjoy aspects of his life with him albeit constrained at the same time.
"For us, all we can do is cling on to the wonderful memories of dad."