The Manchester Arena bomber had "talked about killing people in a public space" for years before he detonated his homemade explosive at an Ariana Grande concert, it has been revealed.
The shocking information was heard at an ongoing public inquiry into the terror attack, where Salman Abedi unleashed a shrapnel packed bomb which claimed the lives of 22 people in May 2017.
Now, evidence given by a prison officer in the enquiry revealed that a current inmate at a UK prison, and close pal of Abedi, claimed he had spoken about "causing harm to others" for a long time.
Abdalraouf Abdallah, a convicted terrorist recruiter who is serving time at HMP Wakefield, had opened up to the officer after learning of the attack.
The prison officer, who cannot be named for legal reasons, was referred to in the hearing as PO1.
During the five-minute chat, PO1 sat on the prisoner's bed in his cell and was told by Abdallah the terror atrocity was done by "one of his boys".
PO1 also said Abdallah informed him that Abedi had talked for years about harming others but everyone thought "he would never go through with it".
The officer reported the conversation through formal prison channels and provided a written statement to police which said: "Abs said for years the lad had talked about killing people in a public space".
The claims by Abedi's friend follow the shocking revelation of new information about MI5's knowledge of the bomber.
Secret evidence held by the security service was made public for the first time, revealing that an MI5 officer had wrongly assessed key intelligence which could have indicated activity of "pressing national security concern".
The senior MI5 corporate witness to the inquiry disagreed that the intelligence did not indicate such concern.
But the service admitted that based on MI5's current policy, if the same evidence was received now, Abedi would have been investigated as a "low level lead".
The public inquiry also heard that MI5 had not passed on pieces of intelligence to counter-terrorism police and that investigators for the security service had been "struggling to cope" with their workload in the years leading to the attack.
One security service witness said he raised concerns over the "triaging of intelligence" from 2015, saying he was "worried something could potentially get through" due to the amount of information they had to consider.
Members of the victims families, who were at the public inquiry as the new information was unveiled said they were left "shocked and appalled" by what they heard.
Kim Harrison, who is representing 12 of the victims' families, said: "To hear that concerns had apparently been raised with superiors regarding the triaging of intelligence, including worries that something could get through due to the volumes of documents being considered, is difficult to swallow."
Abedi had flown to Libya in April 2017 and returned to the UK in on May 18th, five days before the attack.
He was never stopped or questioned at the border when he landed at Manchester Airport.
Chairman of the public inquiry Sir John Saunders asked a senior MI5 witness to consider the "hypothetical scenario" that they had received further context with two pieces of intelligence which were not properly evaluated prior to Abedi flying to Libya.
When asked if they would have arranged for police to stop and search the would be bomber in that case, the witness replied "yes".
The inquiry also heard a document was found which indicated that, several years before 2017, the bomber was considered for referral to the de-radicalisation scheme Prevent, but it was decided not to take any action, the BBC reported.
A letter was written to counter-terror police by an MI5 officer in May 2015 indicating that a security service team were considering opening an investigative lead into Abedi and another individual, but this did not happen.
Between June 2015 and August 2016, as part of another investigation, intelligence was received in respect of Abedi, who was being treated as an MI5 "subject of interest" but was not formally opened as one.
This meant that the formal process and assessment of presented by an individual would not take place.
Over 10 days of closed evidence hearings in November last year, information and processes handled by MI5 in respect of Salman Abedi were reviewed.
As well as the above, a written summary of those hearings revealed concerns that the IT system used by MI5 was "clunky" and "hit and miss".
The inquiry heard the "system for triaging unsolicited intelligence was admitted to be a bit haphazard, and the system has since been changed".
It was also revealed that police acknowledged there was an "unacceptable" delay in analysing intelligence relating to Abdallah's illicit mobile telephone in prison, which was used to communicate with Abedi in the months before the bombing.
Although the mobile had been seized in February 2017, officers didn't get phone bills for the device until June that year, after the attack had already happened.
Abdallah gave evidence at the public inquiry back in November, when he claimed he had no idea what Abedi had been planning.
He told the chairman: "None of my friends, anyone, had any idea what's going on in Salman's head."
Anonymous prison officer, PO1 said Abdallah "seemed bothered" in December last year - days after he had given evidence at the inquiry.
PO1 said: "He was sat in his cell just watching telly. I went in and sat on his bed. I said 'right Abdul, what's on your mind?'."
PO1 said Abdallah didn't refer to Abedi by name, but said that over a period of years, the person had "spoken about causing harm to others".
He said Abedi spoke about it "so often" it wasn't "taken seriously" and dismissed as hearsay by those who knew him.
The prison officer claimed Abdallah hadn't spoken about him before he was called to give evidence at the inquiry, the ManchesterEveningNews reported.
As a result, PO1 said he believed Abdallah did not know who was involved in the Manchester attack - the reason why he reported the conversation because of the "close boys" comment.
