Paul Humphries is on trial at Winchester Crown Court for the murder of John Willdig in Morris Road, Southampton

A murder trial at Winchester Crown Court heard how John Willdig was outside ex-girlfriend Caroline Jarvis' home when her tenant Paul Humphries saw “red mist’ and attacked the defenceless 70-year-old by plunging a knife into his throat and back.

William Mousley QC prosecuting, said in the moments leading up to the killing, Mr Willdig was arguing with Ms Jarvis.

This was outside her house on Morris Road, the Polygon, Southampton, and where Humphries rented a room.

The trial heard how Humphries came downstairs after being phoned up by Ms Jarvis asking him to not let Mr Willdig in to the house.

After Ms Jarvis went inside, Mr Mousley said Humphries was seen to stay outside.

Jurors heard that Humphries then dodged a punch from Mr Willdig.

A passing pedestrian was then said to have heard a male voice in their direction say “if you do that again I am going to punch you” and then “I really am going to kill you”.

Mr Mousley said: “He then saw a man in the doorway of 1 Morris Road who he recognized as Paul Humphries. The argument was continuing.”

Shortly after he told jurors that Humphries pulled a knife and stabbed Mr Willdig, pictured below.

Bleeding heavily, the pensioner managed to stagger a short distance along Morris Road, leaving a trial of blood in his wake.

The court heard how he then collapsed and that a neighbour called an ambulance while residents rushed to help him.

He was taken to Southampton General Hospital where he died at 11.10pm, just under one hour after he was stabbed Mr Mousley saida post-mortem examination found that Mr Willdig had two wounds to his neck, one of them severing an artery.

Three more were on his back – one of them piercing his left lung.

Wounds were also found on his hand, which Mr Mosley said came from fending off his attacker.

Jurors were told that Humphries then fled without calling the emergency services, heading towards his mum’s home in Oakley Road, Shirley.

On his way, Mr Mousley said Humphries then hid an 8.7 cm lock knife in a bush in Raymond Road.

Arriving at his parents’ home, he said he then washed his blood off his hands and arms before telling his dad that he had stabbed Mr Willdig.

The knife allegedly used to stab Mr Willdig

Earlier jurors heard how Humphries suffered from paranoid schizophrenia.

Humphries denies the murder and the court heard how his defence was that he was mentally ill at the time and did not intend to kill the pensioner or was responsible for his death.

But Mr Mousley said: “He quite deliberately and indeed viciously took the life of a retired man in his 70s who was unarmed and presented no serious threat to him.

“The prosecution say the true explanation for the attack was not his mental illness – but anger motivated by malice towards John Willdig, perhaps following a half hearted attempt by Mr Willdig to punch him."

Jurors were told how after arriving at his dad’s house and telling them about the stabbing, he said he wanted to be sectioned.

Without calling the police, Mr Mousley said Humphries' parents took him to Antelope House psychiatric unit in Southampton, where he was examined.

Mr Mousley said he told the unit that John Willdig provoked him and that he was in a "red mist" and that he would rather be in hospital than prison.

He said: "It seemed to the two women he spoke to as if he had a plan to be sectioned."

The police were called. Humphries told police that he had been suffering delusions, the court heard.

• Jurors were told how Humphries had developed mental illness while at university in 2003.

They were told how he went on to be diagnosed with paranoid schizophrenia which would blight his life.

His defence team, the court heard, will argue diminished responsibility because he was mentally unwell at the time of the stabbing.

Yesterday he appeared in court flanked by nurses and paramedics who will stay by his side throughout the trial.

But Mr Mousley claimed that Humphries knew about the law regarding mentally ill people and being responsible for crimes.

He added: “His actions immediately after killing Mr Willdig were well thought out.

“He was calm, organized and had a plan to avoid all responsibly.

"He showed no sign and made no mention of suffering some sort of delusions until he was questioned by police.

“The simple truth was that he stabbed John Willdig to death in the red mist of anger which had fallen upon him the moment he knew Mr Willdig was outside the house, causing him to pick up a knife and then to kill him.”

But the court also heard that Humphries had a criminal past.

It was told this included being found in possession of two knives on Southampton Common in 2004.

Prosecutor William Mousley QC said shortly after Humphries assaulted John Willdig in a pub leading to “bad feeling” between the two from then on.

Humphries, of Morris Road, denies murdering Mr Willdig on June 23 of last year.

Proceeding.