A man accused of murdering a fellow train passenger was paranoid schizophrenic and struggled on public transport, a court has heard.
Lee Pomeroy, 51, was stabbed by 36-year-old Darren Pencille five minutes after boarding a London-bound train at Guildford, Surrey, on January 4 with his 14-year-old son, the Old Bailey has heard.
Jurors have previously been told that a row erupted between the IT consultant and Pencille over the blocking of an aisle.
Ingrid Robertson, the defendant's mother, told the court that when her son was in his 20s she was told he was paranoid schizophrenic.
She said he had been admitted to hospital on a few occasions, had a "fear of crowds", and struggled on public transport - sometimes ringing her in a panic saying he "needed to get off quickly".
"He always thought people were looking at him or wanted to do something to him," Ms Robertson told the court.
Forensic pathologist Dr Olaf Biedrzycki told the jury that Mr Pomeroy had a number of knife injuries including a 10cm deep stab wound, as well as defensive cuts to his hands and arms.
He said Mr Pomeroy had a 6cm deep wound to the left side of his neck, with the knife having cut his jugular vein and carotid artery.
The court has previously heard how Mr Pomeroy, who was due to turn 52 the day after the "quick and frenzied attack", was stabbed 18 times in 25 seconds.
Forensic pathologist Olaf Biedrzycki told the jury Mr Pomeroy had a number of knife injuries including a 10cm-deep stab wound, as well as defensive cuts to his hands and arms.
He said Mr Pomeroy had a 6cm-deep wound to the left side of his neck, with the knife cutting his jugular vein and carotid artery.
"That essentially means that you would have to have instant, immediate surgery in theatre to have any chance of surviving," he said of the neck wound.
Afterwards, Pencille's girlfriend, Chelsea Mitchell, 27, allegedly picked him up and bought hair clippers and razors for him to change his appearance.
Pencille, of no fixed address, denies murder, and Mitchell, of Farnham, Surrey, denies assisting an offender.
The trial continues.