More than 1,000 messages between a 'Salman' and a now-convicted terrorist recruiter were discovered by police in 2014 in a counter-terror operation, but the person wasn't identified as bomber Salman Abedi until after he murdered 22 people at Manchester Arena in 2017, the public inquiry into the atrocity was told.
Some exchanges between Abedi and Abdalraouf Abdallah were 'capable' of revealing Abedi's extremist mindset, the inquiry heard on Monday.
Abedi sent 'selfie' images of himself to Abdallah in mobile phone messages, others referenced his full name and there was also a video of him.
But the information was not highlighted to a counter-terror policing intelligence unit, the inquiry heard.
The detective who led the 2014 probe agreed the 'Salman messages' should have been 'lifted out' of that operation for separate 'intelligence development'.
Paul Greaney QC, counsel to the inquiry, asked retired GMP Detective Inspector Frank Morris: "Do you agree, not with the benefit of hindsight, that where you have a person communicating with someone you believe to be a terrorist who is expressing a similar extremist mindset to them, that something should be done at the very least to find out who they are?"
"Yes," replied Mr Morris.
Mr Morris said 'it would not have been the hardest thing to do to find out his real identity' and agreed that had Abedi been identified, the link would have been available to law enforcement agencies.
A Prevent referral could have been considered and Abedi could 'possibly' have been interviewed, he added, but there was no 'intelligence submission' made to the 'operations intelligence management unit' which ran alongside the 2014 terror investigation.
The inquiry has already heard that in the July - four months before police found the messages - Abedi was 'closed' by MI5 as a subject of interest.
Inquiry chairman Sir John Saunders said he would reach a conclusion over whether a Greater Manchester Police intelligence unit 'should have found things out which they didn't'.
The exchanges were recovered from a mobile phone seized from Abdallah in November, 2014.
He was convicted of assisting others in committing acts of terrorism by facilitating travel to Syria and jailed in May 2016 for nine-and-a-half years.
In 2014 under Operation Oliban, police were investigating several men suspected of travelling to Syria for extremist activity who held allegiance to Islamic State, the inquiry heard.
The 'supportive mindset evidence' used in the subsequent prosecution of Abdallah was referenced at the public inquiry on Monday.
Mr Greaney said between November 5 and 28, 2014, there were around 1,300 contacts between them - more than 40 a day.
One objective of Operation Oliban was to identify any 'like-minded associates who may share extremist views or aspirations'.
Temporary Detective Inspector Paul Costello, giving evidence, said there was a wider intelligence team in the background assessing information gathered regarding other individuals who emerged as part of Oliban.
He accepted there was 'regular contact' between 'Salman' and Abdallah - and there were 'aspects of the communication that caused me concern in terms of his mindset'.
Abedi, on November 12, 2014, sent Abdallah a You Tube clip of an Islamic chant saying: "Oh the soldiers of sacrifice advance forward. Prepare the young men for the day of the call. Restore authority back to the rightness and crush the stronghold of the enemies' soldiers."
He also described non-Muslims as 'dogs' and 'Khuffars'.
The contact was saved as 'Salman' in Abdallah's hone and the number being used ended 3458.
On November 18, a further conversation referenced 'martyrdom'. Abedi said in one message: "Allah willing, the real meeting would be on the Resurrection Day."
TDI Costello said he believed the messages to mean Abedi was 'praying for Abdalraouf's intention to become martyr himself'.
Sir John asked him whether he was thinking 'I think we need to be finding out who this Salman is and investigate him?'
Abedi, said TDI Costello, in one message sent a picture of a Dinar coin minted by ISIS - and called the group 'terrorists'.
And in another message, the inquiry heard Abedi told Abdallah to 'leave it' and that he was 'going too far'.
TDI Costello said Abdallah didn't engage Abedi to go to Syria to fight - and Abedi made no reference that he wanted to do that.
"There was reassurance to me that that would be further looked at elsewhere from an intelligence perspective," said TDI Costello of the 'Salman' messages.
"The messages were there... for others to make an assessment on what else those messages could mean."
In 2015, there was information held by the phone company linking the 3458 number to Salman Abedi, the inquiry was also told.
"There was enough information within the device, alongside with some modest police investigation methods, that could have identified Salman Abedi as the user of that phone at that time, yes," said TDI Costello.
Mr Morris said: “There's nothing extraordinary in these text exchanges that we did not see in other operations.
"It went to the Crown Prosecution Service, they did not ask. Nobody ever asked who this Salman was.
"So with hindsight, of course it [the messages] should have been put in, but at the time I did not think it should have been."
He added that 'four or five people', including detectives, intelligence analysts and himself, were aware of the information but did not flag it up for further inquiries.
John Cooper QC, for a number of the bereaved families, said they do not know how it was processed, who was responsible, 'what steps were taken' and 'what they did with it' in terms of the information.
Mr Greaney said: "That unit did not identify that the 3458 number related to Salman Abedi. That discovery was only made after the Arena attack."
TDI Costello said he would have expected anything found to be relevant to Operation Oliban in terms of the Salman messages to be 'fed back' to him.
"Knowing what I know now I would do anything back then to see if it would help to prevent this attack," he said.
The inquiry continues tomorrow.
