A former child soldier has been locked up indefinitely after killing a stranger in a “ferocious” knife attack in London’s Oxford Street.

Tedi Fanta, 27, was on bail when he armed himself with a knife and travelled to London from Swansea in South Wales, where he was living at the time.

Shortly before 8pm on July 1 2021, he brandished the weapon and jumped on retired civil servant Stephen Dempsey, from Leigh, from behind outside the Microsoft store in Oxford Street.

Two passing skateboarders leapt into action and hit Fanta with their boards in a bid to disarm him, the Old Bailey was told.

They then helped to restrain the attacker until armed police arrived, while other members of the public tended to the 60-year-old victim, who was visiting the capital from south Essex.

When police arrived, Fanta was noted to be speaking in an “incoherent manner” and had a head injury from a blow from a skateboard which was checked in hospital.

Mr Dempsey, who was born in Belfast, had suffered four stab wounds and died in hospital later that night from a knife injury to the chest.

Prosecutor Caroline Carberry KC said Fanta had carried out a “frenzied and fatal attack”.

She told the court: “He is seen carrying out a ferocious, random and unprovoked attack on a helpless and unsuspecting member of the public.

“His victim could have been anyone who was in close proximity to him during the course of that day in central London. Sadly for Stephen Dempsey and his family, it was him.”

Because Fanta, who was suffering from paranoid schizophrenia, was deemed unfit to stand trial, jurors did not have to determine his guilt – only if they were sure he committed the acts he was accused of, Ms Carberry said.

They deliberated for less than an hour on Wednesday to find he had had a knife and carried out the murder.

The court was told Eritrean-born Fanta, who arrived in Britain in 2014, had previous convictions for criminal damage and assaulting a police constable and emergency worker, and was on bail at the time of the killing.

Ms Carberry said he was arrested on June 18 2021 – days before the killing – for “brandishing a saw” in Swansea.

He was bailed by police for that offence to appear at Swansea Magistrates’ Court.

In a victim impact statement, Mr Dempsey’s sister Kathleen Dempsey said her brother was an “unassuming” man who had lived in Leigh since he was a child.

She said the retired civil servant had a “brilliant mind” and a “dry sense of humour” and loved live music and languages, particularly French.

Mitigating, Patrick Upward KC said Fanta was conscripted into the Eritrean army aged 12 or 13.

In the years of conflict that followed, the defendant was shot and tortured, Mr Upward said.

He eventually sought sanctuary in the UK and was granted refugee status but “by then the damage had been done”.

Mr Upward said Fanta was a “very, very ill young man”.

Judge Michael Topolski KC handed Fanta a hospital order without limit of time.

He said Fanta launched a “random and wholly unprovoked attack” and praised passers-by who went to Mr Dempsey’s aid.

He said Fanta had made seven court appearances in the past and been sectioned in 2020, adding: “This defendant slipped through the system unnoticed, uncared for, untreated and very dangerous.”