THE Streatham jihadi was being watched by TWENTY armed cops for 40 minutes before he managed to steal a knife and unleash his bloodthirsty attack.
Sudesh Amman, 20, was shot dead by undercover officers 60 seconds after he stabbed his first victim, the Met Police said.
The extremist, from Harrow, North London, stabbed two people with a 10inch knife he had stolen from a shop.
However, despite confirming details of the attack and Amman’s death, police have refused to explain how the 20-year-old managed to grab the blade without officers noticing.
It has been reported that that the crazed knifeman was being tailed by a team of 20 to 25 armed cops from Scotland Yard's elite SO15 unit.
The jihadi, who had been released from prison on January 23, was also wearing a fake suicide vest which police also failed to spot.
He had been jailed for three years and four months in 2018 after pleading guilty to having extremist material including bomb-making manuals.
STOLE KNIFE AND UNLEASHED HELL
Yet, he was freed to walk the streets of London after being released automatically half way through his prison term despite fears over his extremist views.
In fact, it has emerged authorities believed he needed round-the-clock surveillance and officers tasked with watching him were told to arm themselves because he was considered dangerous, sources told the Guardian.
Police said plain-clothes cops monitoring Amman failed to spot his fake bomb vest because it was hidden under his clothes.
They also said he had been in a shop on Streatham High Road for 60 seconds before he grabbed a knife and unleashed his attack.
In a statement, the Met Police said: "The time from him entering the shop to beginning his attack outside was approximately 60 seconds.
“Police officers responded, fatally shooting him within approximately 60 seconds of him beginning to attack people.'
"An operation was launched which included armed surveillance officers.
"Revealing details of this surveillance operation could undermine police tactics used to investigate terrorists and other criminals across the UK, so it is right that we do not expand on this further at this time."
GONE IN 60 SECONDS
They added: "Armed officers, who were part of a proactive counter-terrorism surveillance operation relating to the attacker, were following him as he left an address in the Streatham area at shortly after 13:20hrs."
Amman stabbed two people- both of whom are expected to recover from their injuries. A third person was injured by glass following a police gun blast.
The ISIS-supporting jihadi, who was only a teenager when arrested, was jailed for possessing and distributing terrorist documents.
He urged his then-girlfriend to behead her own parents and revealed he wanted to "purge society" after pledging allegiance to ISIS.
NO LIKEY THE LIGHTYFamily furious after two lampposts appear in front garden of £400k home
MAID OF MONEYNaked cleaning boss silences critics who said she wouldn't do the job herself
WILD WEST ENDWoman flashes bum as she wrestles pal who called her fat in Leicester Square
HAUNTED TO DEATHGran found dead after being tormented by daughter murdering grandchildren
GOTTA BEEB KIDDINGTV Licence rises to £157.50 - months before free ones end for over-75s
FEBRUARY FREEZEUK weather forecast - SNOW and 'danger to life' 80mph storm to hit Britain
Amman, who once dreamed of being a biomedical scientist, also told her he "preferred the idea" of a knife attack rather than using bombs or acid.
In other messages, the jihadi asked if he could deliver a knife to his girlfriend's home and said ISIS was the best thing to happen to Islam.
Just hours before the terror attack, he had called his mum and told her he wanted his favourite mutton curry.
Raids are now being carried out in Streatham at his bail hostel and Hertfordshire.