Confusion over whether a gunman was at the Manchester Arena bombing meant fire engines arrived more than two hours after the blast, an inquiry was told.
Paul Greaney QC said the inquiry would need to consider “whether a better response by the emergency services would have saved more lives”.
Twenty-two people were killed when Salman Abedi detonated a suicide bomb.
Almost three years before the May 2017 attack, police seized evidence which showed Abedi talking about martyrdom.
Phone analysis revealed discussions with British-Libyan national Abdalraouf Abdallah, convicted in 2016 of helping others to reach Syria, the inquiry was told.
Abdallah’s phone showed Abedi, who went to visit him in prison, had been in contact in the months leading up to the attack.
In February 2017, Abdallah was found to be in possession of an illicit phone which had been used to call Abedi.
Mr Greaney said the relationship between the pair was of “some significance”, and investigators were “determined to get to the bottom of it”.
But Abdallah had refused to answer any questions put to him by inquiry staff when they visited him in prison this year, he said.
The inquiry will also examine what intelligence and information was or should have been available to security service MI5 and the police about Abedi.
On 1 May 2017 Abedi had been assessed as meeting the threshold to be considered for further investigation by MI5.
He was due to be considered for referral on 31 May 2017 but “tragically this was overtaken by matters nine days earlier”, the inquiry heard.
During the third day of proceedings, photographs of the 22 victims were displayed on a screen as the public inquiry heard their final movements.
Relatives of some of the victims wiped away tears in the hearing room at Manchester Magistrates’ Court, while other families watched proceedings from a nearby annexe.
The inquiry heard how 21 of the victim suffered injuries which were said to be unsurvivable.
But bomb blast experts believe the injuries of John Atkinson, 28, may have been potentially survivable.
The public inquiry, which comes more than three years after the attack, will look at a number of factors including the emergency response to the bombing.
The hearing was told how problems with communication and incorrect reports of an “active shooter” meant fire engines carrying specialist equipment and stretchers did not arrive for another two hours and six minutes after the blast at 22:31 BST on 22 May 2017.
Mr Greaney said the inquiry will have to consider “whether that absence contributed or may have contributed to the loss of life that occurred”.
“There can be no doubt there was a need for such joint working on the night of 22 May 2017 in Manchester,” he said during the third day of the inquiry.
The hearing was told North West Fire Control was first notified at 22:34 BST that there had been an explosion and mass casualties, and police were looking for a second device.
They also received reports, wrongly, of an “active shooter” and some casualties with gunshot wounds.
But there appeared to be confusion about whether Greater Manchester Fire and Rescue Service (GMFRS) should follow procedures based on the incident being an explosion or a terror bombing.
Station manager Simon Berry, of GMFRS, was told a rendezvous point was arranged with police at Manchester Cathedral nearby, but this was rejected in favour of a different “muster point” three miles away from the arena.
This decision would be “critical” to the understanding of how the fire service was delayed so long in deploying to the arena, Mr Greaney said.
An expert report on GMFRS’s response to the attack found it “inadequate and ineffective” and said there was a lack of effective leadership, though “no single individual” was responsible for the failings.