The former Mayor of London spoke out on Tuesday as a picture emerged of the supposed ‘ringleader’ of the van and knife rampage, Khuram Butt, posing in his London Underground uniform.
The photo, which shows the mass-murderer posing in a hi-viz vest at West Kensington station in May 2016, emerged as Johnson said MI5 have questions to answer about the monitoring of the terrorists behind the attack that claimed seven lives.
Butt, 27, who was reported to police twice before the London Bridge attack, was named as one of the perpetrators on Monday, along with Rachid Redouane. The third attacker was identified on Tuesday as 22-year-old Yossef Zaghba.
Butt, who last year appeared in Channel 4 documentary, The Jihadis Next Door, was investigated by counter-terror agencies in 2015, but was “prioritised in the lower echelons” after officers reportedly found no evidence to suggest he was planning an attack.
Johnson, the former mayor of London, told Sky News: “People are going to look at the front pages today and they’re going to say ‘how on Earth could we have let this guy or possibly more through the net?’
“What happened, how could he possibly be on a Channel 4 programme and be committing atrocities like this?’
“That is a question that will need to be answered by MI5, by the police, as the investigation goes on.”
According to reports, Butt, who was married with two young children, worked at Westminster and Canada Water stations and had access to tunnel under the House of Parliament. MailOnline said he was sacked for poor attendance.
Butt held the position despite having featured in the documentary and being probed by police a year earlier, something that now, causes his former workmates concern.
One told the Mail: “It was well known that he had appeared in this extremist documentary - but he was asked to leave London Underground not because of that, but due to poor attendance.
“We are now asking ourselves if he was planning something on the job? The intel he will have picked up about Parliament, and the movements of MPs travelling through the station, would potentially be of great value. Maybe he was planning some sort of spectacular there.”
The source, who the website did not name, said Butt’s other duties included working as part of a Station Response Team staffing special events such as the football at Wembley Stadium.
“He was a very quiet and unassuming guy. I spoke to him at length about life and his beliefs. He was definitely religiously observant, but seemingly no more than anyone else,” the former colleague said.
Transport for London has confirmed Butt, who went by the nickname, Abz, worked there from May to October last year.
It has also since emerged that Butt had links to a key contact of Mohammed Siddique Khan - one of the 7/7 suicide bombers, who killed 52 people in London 12 years ago - and had abused a Muslim official over the death of Lee Rigby.
Mohammed Shafiq, chief executive of the Ramadhan Foundation, said on Monday evening that he was abused by Butt after condemning murderers Michael Adebolajo and Michael Adebowale over Rigby’s death in 2013.
Shafiq said he was “abused” by Butt, who was in the company of Anjem Choudhury “the well known extremist and terrorist sympathiser”.
Butt, Shafiq said, called him a “murtad” - which means a traitor in Arabic - and accused him of being a government stooge “when I confronted Anjem Choudhury about him supporting terrorism and my public campaign against Lee Rigby’s murder”.
He said police attended the incident and Choudhury, Butt, and two other men were escorted from the scene.
Shafiq added: “It is clear that Anjem Choudhury and his band of terrorist sympathisers were known to the police for many years. Many of us in the British Muslim community have been demanding action against these extremists to no avail. I am not surprised that Khuram Butt carried out the terrorist attack and there are serious questions for the authorities.
“As in the Manchester terrorist attack, members of the Muslim community are reporting their suspicions about potential extremists which reinforces the strong links between the Muslim community and the police.
“What is clear that Anjem Choudhury, Khuram Butt and their group of terrorist sympathisers have been known to authorities and nothing was done for years.
“I call for an immediate investigation into what the police knew, what was done and why action was not taken against them.”
In another twist to the story, according to the Times, Butt’s brother, Saad Butt, received funding for his part in the Prevent programme, which is aimed at tackling violent extremism.
Butt’s family reportedly asked to be left alone to “grieve in peace” on Monday as it emerged the terrorist held a farewell barbecue at his flat in Barking before committing the atrocity.
Meanwhile, an illford UFC gym where Butt trained, the Ummah Fitness Centre, has closed due to media attention and “unforeseen circumstances”.
The gym was keen to distance itself from the terrorist and in a notice posted outside said, “there is never any justification for indiscriminately killing civilians”.
The notice said Butt “did occasionally” train at the gym which is a “welcoming and open part of the community”, but gym managers had noticed anything “of concern” about him.
“In these challenging times it is important we all stand united, we must avoid scapegoating any part of the community.”