The fire that gutted a house and led to the grim discovery of three bodies in Canberra's north was deliberately lit, police say.
ACT Policing also confirmed on Tuesday they released a man after questioning on Monday, but no charges have been laid.
Police have yet to formally identify the bodies, which were discovered after fire crews rushed to the Bonner house as it was engulfed in flames just after 9am on Monday.
Neighbours said a mother and two children lived at the Peter Coppin Street house, but Detective Superintendent Scott Moller said the formal identification process would take some time yet.
"We can say that after our investigation last night, that the fires were deliberately lit," he said on Tuesday.
"It's a difficult scene, there's been a fire in there...it's a horrific incident…and it has a significant impact on all the emergency services that attended."
Detective Superintendent Moller said it was still too early in the investigation to speculate on the circumstances surrounding the deaths, but fire accelerants were likely used across multiple "seats of fire" in the house.
"There's a number of enquiries...and leads that we're following. No one is in custody at this stage," he said.
Firefighters discovered the bodies inside the house while battling the blaze on Monday.
Once the fire was out, crews had to ensure the building's structure was sound before a second search could begin, Superintendent Moller said.
"Their belief was they were deceased," he said.
The locations of where the three people had been found inside the house, as well as when they died, would form part of the investigation.
"We are investigating all avenues, this investigation is complex, it's going to be a significant investigation for us and it will be going for some time."
Next of kin have not yet been identified.
On Tuesday, the street in Bonner had reopened as forensic teams continued to shift through the remains of the burnt out house.
Detective Superintendent Moller said police had spoken to "lots of residents" in the neighbourhood who were now helping police. Many had witnessed dark plumes of smoke rising from the house the morning of the fire.
Several neighbours expressed their shock at the tragic news and said the family who lived there had mostly kept to themselves.
Community Housing Canberra confirmed it owned the property and leased it at 75 per cent of the rental market rate.
Chief executive Andrew Hannan said the company was liaising with ACT Policing, which now had control of the five-year-old house constructed through the ACT government's land rent scheme for affordable housing.
CHC, which owns and manages multiple properties in Bonner, leases its stock across Canberra for 12-month terms to low- to moderate-income earners.
"The first concern is for the tenants and for their families," Mr Hannan said of the fire.
"Our thoughts and wishes go out to the family and friends and all directly impacted through this terrible tragedy."
Salvation Army volunteers were knocking on doors Tuesday morning, to check on the welfare of those inside.
Major Bob Garven, who is also a chaplain for the ACT's fire brigade, said the incident was "tragic for the whole street".
"We sometimes doorknock and offer people counselling and such after things like this, especially this one being such an unusual tragedy.
"When all of this dies down, the neighbours will still come out and go to work every day and see the house and be reminded."
He said firefighters who attended the scene on Monday were debriefed and provided with counselling.