INTERVIEW
He is a lieutenant-colonel, but works in a laboratory. Guillaume Cognon, head of the environment-fire-explosives department at the IRCGN, the gendarmerie's criminal research institute, conducts daily technical police operations to determine the causes and origins of the fire. Work in close collaboration with the other investigators, but also the professionals of the forest and the fire-fighters, which allows to regularly unblock the investigations. Indispensable to, of course, determine the truth, but also prevent other fires. For Europe 1, Lieutenant-Colonel Cognon agreed to go into detail about his job.
What are the first things investigators do when they arrive at the scene of a fire?
The idea is to arrive as quickly as possible. The sooner we arrive at a burnt site, the more likely we are to keep track of traces and clues. It must be realized that a fire is a crime scene in its own right. We have a systematic investigation method. The first thing is looking for the area of origin of the fire. It is crucial, it is necessary to be able to delimit the zone of departure of fire so as to make the most advanced investigations in this zone. In the case of forest fires, it is difficult because you are quickly on an area that exceeds several tens or hundreds of hectares.
How then to delimit this starting area?
We will use drones, search dogs, a helicopter. On large fires, we do not see much at ground level, we must take the height to follow the reverse path of fire. The idea is to use videos, photos and air assets to remove all areas that are not the cause of the fire. Then, we will do research, excavation, sifting [grid a zone to make a systematic investigation] to further restrict the starting area and find traces like butts, incendiary bottles. The fire has the disadvantage of hiding many traces and clues, it makes a lot of use for observation and reconstruction.
Then begins the second phase of investigation ...
The second phase is the explanation of the trigger. For a fire to take, you need fuel, oxidizer and a source of energy. The fuel, in the case of a forest fire, it will be the trees. Oxidizer is the oxygen of the air. And it is on the source of energy that we will look. It can be natural, it can be lightning. It can also be related to equipment in operation or the emission of a flammable product. This is what will help to move towards a human hypothesis.
What can be the cause of a fire?
There are four types: natural causes, causes related to technology, so a device that has malfunctioned for example, human causes and the indeterminate cause. Whatever the type of fire, the key for us is the search for causes. This is what will help determine the truth and reduce the number of fires. So we will never get there if we do not tackle the causes. For human causes, we have two cases. We have the chance cause: the person is present on site but did not do it on purpose. And the deliberate cause, where there is a kind act. The difficulty is to distinguish between the two. The difference is that on a casual human cause, the person usually leaves more traces.
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How to find traces in case of arson?
You are going to take soil samples from the area you suspect to be starting fire to look for flammable products that would have permeated it. In the laboratory, it is determined whether there is presence or absence of such a product. We are able to implement particularly sensitive analytical techniques. In the context of flammable products, it is possible to distinguish between all commercial petroleum cuts: alcohol, white spirit, diesel, kerosene, oil, etc.
How do you work with the other services of the gendarmerie and the police?
It's a real team work. There are very strong partnerships between the police and the gendarmerie, but also the foresters and firefighters. We, along with the scientific part, confirm or refute the hypotheses of the investigators. The firemen have a very useful knowledge of fire, and the foresters know the fire from the field. They know the types of trees, the vegetation, the topography, and the spread of fire is easier to explain with this knowledge. 1,000 dossiers are processed per year at the fire laboratory. And whereas twenty years ago, each expert worked in his own corner, we now have an increase in multidisciplinary expertise. In a case of finding a corpse in a burned vehicle, for example, fire investigation work can find traces, documents or even DNA. We sometimes give elements to the fingerprint department, the biology department ... and even put a name on a suspect.