Manchester Arena bomber Salman Abedi was seen acting suspiciously and was reported to a steward before he detonated his device, it has emerged.
A member of the public raised concerns about Abedi before the bomb went off and killed 22 people on 22 May 2017.
The detail was revealed in a ruling granting Kyle Lawler the right to gain legal representation at the inquiry into the attack, due in September.
The ruling said Mr Lawler may be "subject to criticism".
The steward, who was 18 at the time of the bombing, had applied for core participant status to gain legal representation and was granted it by chairman of the inquiry, Sir John Saunders.
His written ruling stated the member of the public had "expressed" concern about Abedi, who was wearing a large rucksack in the foyer of the Arena before the end of the concert.
Sir John said "written evidence suggests that [Mr Lawler] saw Salman Abedi... before he detonated the bomb, after suspicions about him had been expressed by a member of the public".
As such, he "may be subject to explicit or significant criticism during the inquiry proceedings or in the report, or in any interim report".
Sir John wrote: "In an experts' report commissioned by me on security arrangements at the Arena... concerns have been raised as to whether Kyle Lawler should have taken more action to draw attention to Salman Abedi's presence and the fact that it was suspicious.
"Kyle Lawler has made statements relating to what happened on the night and is due to give evidence to the inquiry."
He further added his "conclusion is only that Mr Lawler may have played a significant role or may be subject to explicit or significant criticism".
"I am not saying that that will be my ultimate finding, which will depend on the evidence that I hear."