Forensics, how does it work?

Crime scene, DNA, ballistics, the role and excesses of files

Le Monde : 10.01.2010

Forensic investigators are the new heroes of American series – Les Experts – and French series – RIS Police scientifique.

Since 2003, forensic scientists have been using a new molecule that reacts to iron ions in the blood, Bluestar luminol, which is active in the dark

Every week a DNA analysis makes the headlines, as we saw this autumn with the traces found on the envelope of the Grégory case’s corbel, then during the escape of Jean-Pierre Treiber… But how does the real French scientific policy work? To find out, I went into the laboratories of Marseille and Lyon, interviewed investigators, met researchers who are passionate about police investigation work and are bound by their professional code of ethics – and noted the growing, and worrying, importance of DNA files in solving criminal investigations

REPORTAGE (published in part in Le Monde Magazine, January 2010)


We have hair traces in 4522, the case of the robbery with kidnapping of elderly people. Hair was found on the adhesives that bound them.

Coffee in hand, the head of the “Biology” section opens the discussion in a small, low room. The eight heads of department of the Marseille forensic laboratory, engineers and former doctoral students, dressed very casually, meet for the morning’s overview – the “demand review”. Philippe Shaad, the director, the only one wearing a tie, looks stern and says: “We have to try to prioritise. “

That morning, 16 files and 58 coded and numbered seals arrived for biology alone, transmitted by police services in a hurry. Most of them are from robberies and burglaries. There are several DNA samples from ‘individuals’ (the police always say ‘individual’), bloodstains and a swab from a telephone cable.

-The other emergency is 4777, the homicide with a presumption of rape,” continued the Biology Officer. We have 21 stab wounds, blood. The body has been moved, we should see if we can find any plants. He was outside for a long time, and as it has rained a lot, I’m afraid that the DNA won’t tell us anything. We should do some more tests, and concentrate on the car, seal it up… maybe we’ll find some usable traces.

-Well, I’ll call the Commissioner,” says the director. He’s feeling the pressure. Speeding up the result is his job – “I have to streamline” he says.

INPS Marseille handles 500 cases per month, thousands of seals

Since the Sarkozy law of 2003 on “Internal Security” and the methodical collection of DNA by the police, requests to the forensic police have soared. “We are moving from the craft to the industry,” explains Philippe Shaad.

The floor is given to the “Fire-explosions”. Big suspense. Because that morning, a heavy gun battle once again made the headlines in Marseille. Machine-gunned in front of the Velodrome stadium” headlines La Provence. What happened?

At around midday, two individuals wearing black helmets fired automatic pistols and Kalashnikovs at a man who was leaving a gym. Ten bullets, head and chest. The man, a former released bank robber, was suspected of having shot a known gangster in September 2007. Revenge, no doubt. Before fleeing, the two assailants set fire to their car. The men of the “fire and explosion” unit are trying to identify the explosive used. If it was a grenade, they will be able to cross-check. If it was a Molotov cocktail, they will analyse the fuses and the petrol.

Why did the killers set the car on fire? To remove traces of DNA. It’s become commonplace,” a sergeant explained. Banditry, large and small, as Vidocq well recounted in his memoirs (1828), has always adapted to advances in police expertise. Today, to eliminate DNA, they “blow up the stuff” as Chéri Bibi used to say.

Now it is the turn of “ballistics” to intervene. The technicians analyse the cartridge cases discovered after the Vélodrome shooting. Each weapon has a “fingerprint”. In Marseille, the police are used to the use of Kalashnikovs by the milieu. Since the fall of the Berlin Wall, it has become the favourite weapon of the small-time crooks of the French Riviera.

New case of the day, toxicology expert causes a stir:

We have a drug rape, with blood on cotton wool. The sample is insufficient. It is not suitable for our analysis.

Director’s ticking. Slowdown in sight. What’s the difference between “narcotics” and “tox” experts? The former deal with seizures of hard drugs that have not been consumed – the port of Marseille was the port of the “French connection” – but also with hashish from Morocco, sold by the small-time kings of the cities – at war with each other. They try to identify the drugs, the cut products, and then compare them with the substances seized in several cases to trace the networks.

The “tox” people confuse drunk drivers, stoned people responsible for an accident, or process substances found in dead people: carbon monoxide, drugs, chemicals, etc. They do forensic work. They do forensic work. What else did the ‘tox’ do on 25 September 2009? Three roadside alcohol tests. The usual.


In France, police experts are not multi-skilled super-cops capable of detecting a micro-trace of blood, conducting a profiling interview of a serial killer and then drawing their weapon faster than Agent Catherine Willows in “CSI Las Vegas”. In fact, the jobs of police investigation, evidence collection and forensics remain separate – unlike in the series “RIS. Police Scientifique”.

When a crime occurs and the investigation begins, the forensic identification officers, the “ijists”, “freeze” the “crime scene” on the spot. Trained for this, gloved, masked, protected, they put up barriers, make sure that no one, journalist or neighbour, comes to pollute the place by spitting or with their shoes. Then they take photographs, make sketches, record clues and DNA samples, which are then placed under seal by the judicial police officer. The investigators then call in the services of the forensic laboratories.

In France, three-quarters of the ‘experts’ are not police officers, but former doctoral students from science faculties, engineers and technicians working for the magistrates and the judicial police. These researchers are also civil servants of a public establishment, the Institut National de la Police Scientifique (INPS), which groups together all the technical and scientific police services: biology, ballistics, trace documents, fingerprints, fire-explosions, physical chemistry, narcotics, toxicology, technological traces, all the ‘forensics’.

French forensic science has a long history. Some historians trace it back to the investigation of the “poisoners of Versailles”, conducted by La Reynie under Louis XIV. But the pioneer was Edmond Locard, Alphonse Bertillon’s colleague, who founded the first technical police laboratory in Lyon in 1910…

We are in the Third Republic, Jules Ferry is educating the countryside, and a republican and positivist impulse wants to make us forget the brutal practices and the political filing of the Second Empire police. Edmond Locard wanted to replace the traditional police search for witnesses – unreliable – with the methodical search for convincing evidence – the constitution of proof – and the obtaining of confessions – “the queen of proofs” often obtained by sequestration and beating (formerly by the dreadful questioning or torture) – and sometimes retracted.

With anthropometry, dactyloscopy (fingerprint analysis) and the search for clues, Edmond Locard set the roadmap for a more objective police force: “No individual can stay in a place without leaving the mark of his passage,” he wrote, “especially when he has had to act with the intensity that criminal action requires…”.

Modern French forensic science was really developed at the initiative of the socialist Pierre Joxe, following a distressing report on the state of the premises and equipment of the technical police

In 1985, he allocated significant funds to them, hired scientists and engineers, and brought together all the laboratories and archive and documentation services. This reunification continued under the Jospin government with the authorisation of DNA sampling and the creation of the National Automated DNA Database (Fnaeg, initially intended for sexual offences and later for organised crime and terrorist cases) and the law of 15 November 2001 on “Daily Security” (LSQ), adopted two months after 11 September.

This law will be said to be liberticidal by human rights associations for having liberated telephone tapping and punished by prison the refusal to take a DNA sample. It founded the Institut National de la Police Scientifique or INPS, a public institution under the supervision of the Ministry of the Interior.

In the opinion of the director of the Marseille laboratory, the separation of police and scientific analysis tasks through the INPS is very important: it preserves the independence of the expertise from police or judicial pressure. The separation of the professions is appropriate because it enriches the investigation. Generally, we hardly know the case we are dealing with. We are objective and neutral. These different views on the same investigation avoid false leads and enrich the investigation. Sometimes, they nuance or counteract the overly fixed “intimate conviction” of a judge or a police officer in a hurry.

In 2004-2005, the appalling miscarriage of justice in Outreau left its mark on the judicial and police apparatus.

Magistrates and lawyers reproached the young judge Burgaud for his fixed ideas, his summoning of children to the police station, his contempt for the defence. The psychological experts, in this case judicial, have accumulated errors of interpretation. The expertise, often called “scientific”, has been discredited. In fact, the expression “scientific police” can be worrying. It seems to imply that this police force is never wrong. That they are armed with an exact science that is always conclusive. That an expert, a psychological or genetic profiler, always tells the truth. But we know that the police arrest one-day suspects, that “false guilt” appears. That “irrefutable” evidence is difficult to establish.
The police and the judiciary have to build up a ‘body of evidence’ to convince themselves of the guilt of an ‘individual’, and experts provide them with ‘investigative evidence’. Sometimes they are wrong. Alphonse Bertillon, the father of anthropometry, gave a graphological expertise of the famous “bordereau” of the German embassy which accused the unfortunate Captain Dreyfus – but he had not written it. In other words, an expert opinion does not establish guilt for sure.

What does the director of the Marseille forensic laboratories think?

We never make a judgment of guilt. We answer a question asked by the investigator or magistrate. What make of car is this paint chip found in the wound of an accident victim? Was this shell casing fired from this weapon? Did this person die by drowning? We can go back to an investigator to discuss how he or she collected evidence, or ask to expand the search. The fact that we are not on either side of the fence, neither police nor judge, guarantees our independence. This is well noted on the journalists’ handbook.


Since 2003, forensic scientists have been using a new molecule that reacts to iron ions in blood, Bluestar luminol, which is active in the dark. Whether the soil has been washed away or the blood diluted a thousand times, there are always a few metal ions left at a “crime scene” – and luminol reveals this by chemiluminescence. Blood traces provide DNA, their projections give ‘morphoanalysts’ clues as to how a blow was struck, how the blood flowed or gushed out.

Many criminal cases have been solved with luminol, such as the sudden disappearance of the Flactif family and their three children in April 2003. But while luminol is an effective detection product, beware of misinterpretation. It also reacts to copper, blood in urine, faeces and sodium in bleach: it could, for example, indicate a walker who has relieved himself in the wrong place. This has happened. All the experts in Marseilles say it: technology is useful for an investigation, it does not give the truth.