An autistic teenager could be seen laughing moments after he threw a six-year-old boy from the Tate Modern viewing platform, a court heard, telling onlookers: “It’s not my fault, it’s social services’ fault.”

Jonty Bravery spent more than 15 minutes stalking potential victims at the London tourist attraction before fixing on a young visitor who had briefly left his parents’ side, the Old Bailey heard.

The well-built 17-year-old, from Ealing in west London, was said to have scooped the victim up “and, without any hesitation, carried him straight to the railings and threw him over”.

The Old Bailey heard on Thursday that Bravery was deemed suitable to visit central London unsupervised on Sunday August 4 2019, the day he attacked the boy, despite a history of violence to social care staff which required him to be under one-on-one supervision.

Mrs Justice McGowan, who will hand down her sentence on Friday, said of Bravery: “Whatever happens, it (the sentence) will be for a very long time.”

Defence counsel Philippa McAtasney said Bravery seemingly signalled his intention to commit such an offence in a secret recording apparently made by care staff.

Hammersmith and Fulham Council said an independent Serious Case Review is under way.

(Bravery) said he had to prove a point to ‘every idiot’ who had ever said he did not have a mental health problem that he should not be in the community

The victim, who cannot be identified because of his age, fell around 100ft (30m) to a platform below, while disbelieving witnesses, including the boy’s parents, challenged Bravery.

The victim’s father originally thought the incident was “a joke” until he saw his son’s severely injured and bloodied body below.

The child’s mother became “increasingly hysterical” and tried to climb over the railings to get to her son several stories below, but was held back by staff, the court heard.

Bravery, who is now 18 and admits attempted murder, was said to “have a big smile on his face” and told the boy’s father: “Yes I am mad.”

Prosecutor Deanna Heer said CCTV captured the incident, then showed Bravery backing away from the railings.

She said: “He can be seen to be smiling, with his arms raised. At one point, he appears to shrug and laugh.”

The court heard Bravery made his way on foot to the Tate Modern, arriving at 2.16pm, having previously scoped out the Shard – Britain’s tallest building – but was unable to afford a ticket.

Witnesses at the Tate said he was “behaving in an unusual way” and was seen to look over the railings near where he would later throw the boy.

Two women, visiting the tourist attraction with their two sons aged eight and 11, saw the defendant “smiling at the children”, the court heard.

The court was told the victim and his family – on holiday from France – arrived at the Tate Modern viewing platform at 2.32pm, having spent the day sightseeing and having a picnic by the river.

CCTV then caught Bravery turning towards the victim’s family, with the boy skipping a little way away from his parents.

Ms Heer said: “As (the boy) approached, the defendant scooped him up and, without any hesitation, carried him straight to the railings and threw him over.

“The CCTV footage shows (the boy) falling head-first towards the ground.”

The court heard the boy suffered life-threatening injuries, and spent more than a month in hospital in the UK before being discharged to a hospital in France.

He remains in a wheelchair, and will require 100% care support until at least August 2022.

Ms Heer said: “Whether he will ever make a full recovery is not known.”

She said Bravery blamed social services when challenged by witnesses moments after the incident.

He was heard to say “It’s not my fault, it’s social services’ fault”, with a shrug, the lawyer said.

Following his arrest, Bravery was said to have asked police if he was going to be “on the news”.

He said he had been “seriously unhappy” recently and that he had to do anything he could to get out of his accommodation.

Ms Heer told the court: “He said he had to prove a point to ‘every idiot’ who had ever said he did not have a mental health problem that he should not be in the community.”

Defence counsel Ms McAtasney said it was “unlikely” her client – diagnosed with Autism Spectrum Disorder when he was five – would ever be released into the community.

She said: “There’s no immediate cure for this defendant’s condition.

“We’re talking about this young man in whichever setting – either hospital or prison – for a very, very long period.

“The likelihood is this young man is unlikely ever to be released.”

Bravery appeared in court via videolink from Broadmoor, at one point sitting on the floor and another with his T-shirt pulled over his head.