Hidden within the soggy rubble and ash of the farmhouse where the Maillys were found dead lies the story of the family's last hours.
As detectives continue posing questions today, arson investigators will be looking for bits and pieces of scorched evidence to help prove the police theory that Francois Mailly killed his wife and three children, possibly with a .22-calibre gun found where the front door of the house use to stand.
It's a daunting task. The 2315 Dunning Rd. fire scene is one of devastation. But the science of fire, of how it behaves, is an established and knowledgeable discipline.
The first order will be to determine the fire's origin and cause.
Fire usually burns outward from its point of origin and, by tracing back that trail, experts can often pinpoint the source of ignition -- a couch, a carpet, a bed -- and reconstruct what happened.
"It's really important that you determine where it started because then you can rule out -- or rule in -- certain things, say electrical or whatever, but you have to know where it started," says Jim Whitaker of the U.S-based International Association of Arson Investigators.
And if there is more than one point of origin, "it most likely wasn't accidental," he says.
Police, meanwhile, say the victims' bodies were severely damaged by the fire. But human bodies are very difficult to burn completely.
As flames consume a body, the fire burns upwards, searching for more oxygen. That will often cause a ceiling or walls to collapse around the bodies and shelter them somewhat, leaving valuable evidence for an autopsy to confirm a cause of death.
Samples of materials will be undoubtedly collected from around the point of origin and sent to a laboratory to confirm that an accelerant, such as gasoline, was used.
Residual traces of a liquid accelerant can often be found in places were liquid can travel easier than air, such as under baseboards, at the outer edges of carpets and under furniture legs, say arson experts.
An accelerant-sniffing police dog might even be brought in. And, investigators will ask, did the first neighbours and firefighters to arrive at the scene smell anything, such as gasoline?
The fire investigators also will be looking for trace evidence in the rubble -- hair, fibre, blood, semen, dirt, dust, shavings, bits of clothing, gunshot residue -- that bolster their theory that Francois Mailly killed his family, then died in the ensuing flames.
What may never be known, however, is why he presumably lit the house on fire.
Arson typically is motivated by revenge, vandalism, concealment of another crime, excitement or profit.
But police found what appears to be a suicide note inside a van outside the house.
What earlier yesterday seemed like the most plausible reason -- concealment -- now does not appear to have been a factor.
Perhaps, as one crime expert suggests, Mr. Mailly simply wanted to destroy everything.