London Bridge terrorist Khuram Butt's M15 investigation was suspended three months before the attack, according to an investigation into even more serious plans.
A senior official who testified when investigating the deaths of the eight victims said that the Ringleader's counter-terrorism investigation had been suspended because he was classified as "medium risk".
The witness, who was only identified as Witness L, informed Old Bailey today that the investigation was suspended from March to May 2017 due to the "available resource pool".
Rachid Redouane (30), Youssef Zaghba (22) and Butt (27) mowed pedestrians before walking through Borough Market on June 3 and stabbing passersby.
Security services received a second anonymous tip that Butt was an extremist before the investigation against him was launched in 2015.
Butt's own brother-in-law passed the first report on him to an anti-terrorist hotline because his views became "increasingly extreme" almost two years before the atrocity, an earlier hearing said.
Terrorist Khuram Butt after being shot by police at Borough Market. Butt and his co-attacker strapped empty canisters to their waist to look like explosives
The van used in the London Bridge attacks mowed pedestrians before crashing into railings outside the Barrowboy and Banker Pub
Witness L informed the court of the investigation The butt was exposed during the "most alarming" period in which MI5 had been in almost three decades.
He said the decision to suspend a series of investigations at this time was made in the face of the unprecedented threat and the pressure on our resources.
During a review evaluating the likelihood that he would launch a lone wolf attack in September of this year, Butt was described as "a medium risk of being a potential single actor and no risk of being a spontaneous or fleeting extremist "viewed.
This despite a 2010 warning of assault and regular collaboration with Anjem Choudary, the leader of al-Muhajiroun (ALM).
Khuram Butt was shot dead by the police on June 3, 2017
Butt came on the MI5's radar in 2015 after pointing out that one person wanted to launch an attack in the UK.
He was spotted at a rally in the Regent's Park Mosque in July of this year before praying in front of an ISIS flag in the park, and was photographed with well-known extremists Shakil Chapra and Mohammed Shamsuddin.
Witness L added: "In my 28 years (in MI5) I can't remember a time as alarming as this."
Investigators could not identify the school where Butt and his assailant taught Zaghba – the Ad Deen elementary school in Ilford, east London – which was run by the wife of the well-known extremist Sajeed Shahid.
Witness L accepted that a potential investigative opportunity had been missed and that the gym that Butt, Zaghba and third attacker Redouane were in, also owned by Shahid, had not been investigated further.
He said, "We tried to get better coverage of the gym, but it didn't work."
The court had previously heard that MI5 received an anonymous tip that Butt was an extremist before an investigation was launched against him in 2015.
Witness L said an informant who specifically asked not to be contacted again contacted the security service.
He said the intelligence agency had "identified a person of the correct age, Khuram Butt, and said he was an extremist."
Rachid Redouane and Youssef Zaghba and Khuram Butt's CCTVs enter Ummah Fitness Center in Ilford, east London, where they exercise regularly every three days before the attack
Redouane, Zaghba and Butt enter their gym. All three terrorists were shot by the police at the scene
This information was released before MI5 launched an official Butt investigation in mid-2015.
He came on her radar in 2014 after being identified as a supporter of the banned extremist group al-Muhajiroun.
The service only found after the London Bridge attack in June 2017 that the information related to the same person.
27-year-old Butt, 30-year-old Redouane and 22-year-old Zaghba killed eight people and injured 48 others in the attack on vans and knives on June 3, 2017.
They mowed pedestrians on London Bridge before accidentally stabbing innocent onlookers at nearby Borough Market.
Jonathan Hough QC, attorney for the victims' death investigation, asked Witness L whether the public should be concerned that the police and MI5's investigation into Butt following a series of mainland terrorist attacks in February 2016 for about a month Europe was exposed.
At the time, it was known that Butt had expressed a desire to launch a terrorist attack in the UK in 2015 and had publicly associated with members of al-Muhajiroun, including the leading figure Choudary.
The authorities also did not know that he had distributed extremist material, some of which could have resulted in criminal charges, and it was considered at risk to travel to Syria to fight for the Islamic State.
Khuram Butt slipped through the network, although he was reported by his own family about extremism and MI5 received another reference to him
The Terrorists' Path on the day of the London Bridge attacks through the city towards Borough Market
Witness L said: “I think this reflects the available resource base. These and similar investigations had to be suspended because there were other investigations. "
The official responsible for policy, strategy and skills in the MI5 international counter-terrorism department provided evidence that was protected from the public and said money was not the only problem.
He told the court: “Money is not the key determinant here. Even if we asked for more money in November 2015, his ability to switch to actually experienced investigators by 2016 would simply not be plausible. & # 39;
He told Old Bailey that a post-attack review conducted by a MI5 manager with an expert group showed that "the Khuram Butt investigation was well and effectively done."
The decision to temporarily suspend the investigation against the 27-year-old due to the resource pressure in February 2016 and March 2017 was "logical and proportionate under the circumstances".
The police have not been "systematically" consulted on the suspensions, but may have been contacted informally, he told the court.
Witness L faces questions about how much MI5 knew about the three attackers on London Bridge before the atrocity, and whether it could have been stopped.
Victims of the terrorist attack were Xavier Thomas (45), Christine Archibald (30), Sara Zelenak (21), Sebastien Belanger (36), James McMullan (32), Kirsty Boden (28), Alexandre Pigeard (26) and Ignacio Echeverria (39 ).
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