Lives may have been saved but for a series of “missed opportunities” to spot and stop suicide bomber Salman Abedi before his attack on the Manchester Arena a public inquiry concluded.

If Islamic State-inspired Abedi had been spotted and challenged, no one could know what he would have done but it is likely fewer people would have died, Sir John Saunders, chairman of the Manchester Arena Public Inquiry said in his report.

Abedi, 22, dressed all in black and carrying a huge backpack containing his home-made bomb, should have been identified as a threat and action taken sooner, after he was reported as suspicious by a member of the public.

Sir John concludes in his report: “Had that occurred, I consider it likely that SA (Salman Abedi) would still have detonated his device, but the loss of life and injury is highly likely to have been less.”

The report, the first of three from the ongoing public inquiry, dealt only with security arrangements at Manchester Arena before the attack.

It criticises security arrangement at the venue, one of the largest and busiest in Europe, at the time of the attack, with both the Arena’s operators, SMG, their security and stewarding sub-contractors, Showsec and British Transport Police (BTP), and employees of all three, responsible for the missed opportunities.

The report states: “I am satisfied there were a number of missed opportunities to alter the course of what happened that night. More should have been done.”

The missed opportunities cited by Sir John were:

– Abedi made a number of trips to the City Room to carry out “hostile reconnaissance” before he detonated his shrapnel-packed bomb, killing 22 bystanders and injuring hundreds more at 10.31pm on May 22 2017, following an Ariana Grande concert. He spent 20 minutes in the City Room, from 8.50pm to 9.10pm, and chose to hide in a “blind spot” not covered by CCTV of the area. Had CCTV picked him up, his bulky clothing, hat and backpack would have raised suspicions and “heightened sensitivity” to his presence. The fact he left, and then returned at 9.33pm to take up position for the end of the concert, represented an opportunity to identify him as a potential threat, which was missed by Showsec steward Mohammed Agha. Abedi again hid in the “blind spot” area of the City Room and had Mr Agha been “adequately trained” it would have led him to report Abedi’s presence out of sight of the cameras. Had the opportunity not been missed it is likely Abedi would have been spoken to before 9.45pm – when the City Room was largely deserted. Sir John concluded Abedi may then have detonated his bomb, or left to return later, but added: “None of these possibilities is likely to have resulted in devastation of the magnitude caused by Salman Abedi at 10.31pm.” Both Mr Agha and his employer, Showsec, bore responsibility for failing to act, the report said.

– SMG’s CCTV “blind spot” was also cited as the cause of “a different but connected missed opportunity” which would have spotted Abedi hiding and could have led to him being challenged earlier.

– An adequate patrol of the City Room by Showsec staff shortly before the concert ended, as they were contracted to carry out, was another missed opportunity, the report said. But it was Showsec workers’ practice not to check the mezzanine area where Abedi hid away from the CCTV cameras. If this had been done Abedi would have been spotted by a patrol.

– Sir John concluded the “most striking” missed opportunity involved a member of the public, Christopher Wild, reporting Abedi to stewards 15 minutes before the explosion. Mr Wild and his partner, Julie Whitley, were waiting to pick up her daughter and her friend. They spotted Abedi and Mr Wild was concerned with his bulging rucksack and worried he might “let a bomb off”. He reported Abedi to Mohammed Agha at 10.15pm, but was “fobbed off”. That Mr Agha did not take Mr Wild’s concerns seriously, and act immediately by reporting the matter to supervisors, was a missed opportunity while there was still time to take “decisive action”.

– A further, connected chance to identify Abedi as suspicious, was missed very shortly after at 10.22pm, just eight minutes before the attack. Mr Agha passed on Mr Wild’s concerns to another Showsec steward Kyle Lawler. The men, both then aged 18, eyeballed Abedi, who appeared to notice and looked “fidgety”. Mr Lawler tried to pass the report through to the control room but could not get through on his radio. His efforts to raise the alarm were not “adequate”, the report said and he instead left the City Room to take up his post for the end of the concert.

– Finally the report said that if a BTP officer had been in the City Room, then Abedi would have probably been challenged earlier. Despite instructions for at least one officer to be present in the room at the end of the concert, none were present from 10pm onwards. Mr Wild’s report of suspicious behaviour would then have been passed to a BTP officer to investigate, causing Abedi either to leave the area – or detonate his device. Sir John concluded: “In either case, it is likely that fewer people would have been killed.”