Alongside police and emergency response crews clearing the explosion site in the downtown core of Lac-Mégantic, Que., a team of forensic investigators has begun the grisly task of recovering and identifying the remains of up to 60 people still reported missing from Saturday's horrific train crash.

The nature of the accident – an extremely hot explosion followed by hours of scorching fires that some witnesses' claim could be felt a kilometre away – will make the Quebec coroner's job very difficult, experts say.

The essential first step, according to Tracy Rogers, a forensic anthropologist at the University of Toronto, will be co-ordination and organization.

"There's going to be a number of different investigative groups trying to access the scene, and there's going to be a lot happening simultaneously," says Rogers.

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Forensic investigators have to systematically comb through the entire accident scene for physical evidence to help identify victims of the explosion. (Canadian Press)

"All of those efforts need to be co-ordinated right away because all these groups are searching for different kinds of evidence."

A primary challenge will be locating human remains among the debris, which is largely all the same colour after being exposed to fire for such a long period, says Rogers.

"Because of the range of conditions that bodies may be found in, it takes a person with a lot of experience to differentiate between what might belong to a human from what is a piece of a building, for example," she says.

The smallest details

Also critical to the initial investigation is what forensic scientists call the "ante-mortem," a file assembled by the police and coroner's office with help from a missing person's family and friends that contains as much information as possible about that individual.

"There are two parts to this: a biological profile and a personal profile," says Kathy Gruspier, a Toronto-based forensic anthropologist with the government of Ontario. 

"Sex, age, race, any information at all helps develop a biological profile of the person. Then there is the personal biology, whether a person had a fractured heel at some point, for example, or any kind of medical appliance in their body," says Gruspier.

'If a person had, say, a bump on the side of their head or a broken rib at some point in their life, an anthropologist can discern that from remains if they are preserved enough.'—Bill Inkster

That information is then compared with any physical remains that can be found at the scene.

According to Bill Inkster, an identification expert at the Office of the Chief Coroner in B.C., even the minutest details can help.

"If a person had, say, a bump on the side of their head or a broken rib at some point in their life, an anthropologist can discern that from remains if they are preserved enough," Inkster says. "It's only circumstantial, but it helps to narrow down who the person might be."

Teeth and bones

In many instances, a dental profile can be used to identify a body, if the investigators have access to dental records from someone's life.

But this technique presents challenges, says Rogers, because it requires that the person had enough dental work to rule out somebody else.

In a scenario like the explosion and fire at Lac-Mégantic, investigators will likely have to rely on DNA samples from what remains there are to identify victims, says Inkster.

"DNA techniques have advanced quite far now and, really, we can get DNA from pretty much any anything, even ancient remains, to do a DNA profile," says Gruspier.

"There may be cases where the DNA is too degraded or contaminated, but certainly we try in any case."

Once a DNA profile is obtained, investigators compare it with DNA taken from a personal item that they believe belonged to that individual, like hairbrush. If that's not available, then the second best option is to use DNA from a relative, says Gruspier.

According to Rogers, it will take much longer to complete the victim identification than it will to collect evidence at the scene because the methodical nature of isolating usable DNA and then ruling out all other possibilities in determining a victim's identity.

Confidence in the investigators

Inkster says that although many of the victims' remains will likely be severely damaged by the explosion and subsequent fire, it's exceedingly rare that investigators fail to find enough physical evidence to identify remains.

"If it was the case that people closest to the blast were completely gone, it would be devastating to the investigators. But it would be a surprise to me, in fact it would be a first for me," he says.

According to Inkster, Quebec is well known amongst forensic professionals for the quality and dedication of its investigators.

"I don't want to estimate how many individuals will be identified or not," he says. "But I will say this, if it's humanly possible to do it, they'll get it done in Quebec."