BALLARAT Police want to speak to three teenagers seen in Broderick Crt shortly before fire engulfed a two storey unit on Sunday night.
Detective Senior Constable Steve Campbell said three people, aged from 12 to 15 years, were seen near the Canadian Lakes unit about 9pm.
He said a witness thought one of the teenagers was wearing rollerblades.
"I'd like these kids to come forward and see if they can assist us," he said.
"Somebody knows how and why and who, and I would urge them to contact us before any further damage is done."
Fire engulfed the nearly-completed, two-storey unit on Sunday night.
The Country Fire Authority sent 25 personnel to extinguish the fire about 10pm, and it flared up about 3.30am Monday.
Det Snr Const Campbell said investigators believe the fire was smouldering for up to an hour before flames became visible about 10pm.
Police were called back to Broderick Crt about 1.45am yesterday when neighbours saw a person enter the house with a what looked like a lighter.
The neighbours saw a white Mitsubishi Magna parked in front of the house. The person was inside the house for about five minutes while the neighbours called police.
Police patrolled the area several times during the morning.
Det Snr Const Campbell said the fire was suspicious but could have been accidental as no accelerants were found.
Det Snr Const Campbell said it was too early in the investigation to tell whether the teenagers were suspects.
McMaster Homes owns the unit, which hairdresser Nathan Tracy hoped to take over in the next two months.
McMaster Homes supervisors John Howley and Andrew Rock inspected and fenced off the unit yesterday.
Mr Rock described the arson attack as "heartbreaking". He said the first floor needed replacing and the unit could require demolition.
The adjoining unit was protected by a fire wall and survived the blaze.
McMaster Homes supervisor John Howley said he did not understand why arsonists had targeted the unit.
"It's been a bit of a pain, they are pretty good looking jobs," Mr Howley said. "You don't know what to think."
Det Snr Const Campbell is also looking into a possible link between the fire and attacks on unfinished buildings in Sebastopol.
He said a spate of fires had been lit in newly-erected house frames in Sebastopol.
"There have been a number of other fires in houses under construction," he said.
Det Snr Const Campbell said he would not rule out any possibility at this stage of the investigation.
"It's very difficult with fires because there are so many possibilities," he said.
People who see anything suspicious should report it to police on 5336 6000 or 000 for emergencies.
Anyone with information about the case is asked to contact Ballarat CIU on 5336 6080 or Crime Stoppers on 1800 333 000.
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