NSW Police say a third boy is assisting detectives with the ongoing investigation into what caused the fire that ripped through a historic inner-city Sydney building on Thursday.
The 12-year-old was in the multi-storey building at the time the fire started on Randle Street, Surry Hills, along with two 13-year-olds.
The two teens had already been co-operating with Strike Force Strontium, set up to investigate the incident, after handing themselves in to two separate police stations late on May 25.
"Strike Force detectives can confirm that three boys, one aged 12 and two aged 13 .… are assisting with inquiries," police said in a statement on Saturday afternoon.
"No charges have been laid and no further information is available at this time."
On Friday, police appealed for others who had been inside the former hat factory to come forward after they were told "other teens" were there with the boys.
NSW Fire and Rescue (NSWFRS) have been monitoring the site, and earlier on Saturday said one of the building's walls continues to move inwards, and fire crews are planning its demolition.
The unstable walls pose a significant threat to public safety, and specialist crews have been assessing them with drones, NSWFRS said.
Acting Zone Commander Grant Rice said the unstable wall had moved 75mm.
He said the inwards movement was positive, as it meant it was less likely to collapse onto the street.
"We've got some high vantage points ... but the drones have been extremely helpful ... with infrared technology," he said.
An exclusion zone remains and nearby residents forced to flee their homes are unable to return until the site was safe.
"Once we get it to a safe level of controlled demolition, that will assist us on our side to get people back into those buildings."
"One external wall has moved 70mm overnight, reinforcing the commitment to maintain the current exclusions zones for community safety," it said.
Firefighters are still unable to enter the old RC Henderson hat factory as "light smouldering from deep within the rubble" continues.
The classic 19th century warehouse was set to be developed into a 123-room hotel but instead, 120 firefighters in 30 trucks battled the inferno from 4pm on Thursday, containing it just before 6pm.
According to police 15 homeless people were in the building the night prior to the fire and all but two have been accounted for.
Police are yet to establish the identity of the missing two people.
At least 100 people have registered as being displaced from neighbouring buildings which were forced to evacuate and many have been provided alternate accommodation through Welfare Services.
Others have made their own arrangements.
They were told to gather essential items, such as medication, while huge cheers greeted some of the pet rescues.
Fire and Rescue NSW Acting Commissioner Jeremy Fewtrell said it was a co-ordinated effort with NSW Police.
"We even had one lady who was due to have a wedding in Hobart, or in Tasmania, and firefighters were able to go and retrieve her wedding dress," he said on Friday.
"That's a very happy bride, I would imagine."
Acting Commissioner Fewtrell said it would become a "really defining point" for the firefighters who battled the blaze.
"The one thing I can guarantee at the end of their careers; this is one of the highlights they will reflect upon."
The factory was sold to developers Hanave in 1978, and was to be transformed alongside the old Ding Dong Dang Karaoke Club, and another adjoining building.
Architecture firm Tonkin Zulaikha Greer won a design competition, and director Tim Greer said they had put six years of incredibly hard work into the project.
The firm was devastated at the loss.
"We were ready to move onto the next stage, which was the building part of the project," he said.
"The original building was complete. It had its beautiful brick facade, it had its beautiful timber floors, big timber posts and bearers, and joists and timber boards."
Mr Greer said it showed why new buildings were now stringently designed with fire safety controls.
