How does the scientific police work?

How does the scientific police work?
(Le Mag de France Bleu Poitou)

(France bleu: January 21, 2022)

“To identify the presence of blood that cannot be seen with the naked eye, because the scene was cleaned before the police arrived, the forensic police use Bluestar to reveal the erased traces”

Television loves forensics, because there are crimes, investigations, motives, and we get to see the daily lives of police officers and forensic scientists.

A short history of forensics

Before the first tools of forensic science, testimonies and confessions were the basis for convincing a suspect of his guilt. Alphonse Bertillon (1853 – 1914) founded the first police laboratory for criminal identification in 1882. He constituted the basis of forensic anthropometry, which allows the identification of people.

Ten years later, Francis Galton introduced systematic identification by fingerprints. Other valuable tools in a criminal case are the presence of traces, photos of the scene and a map of the scene. The forensics team makes observations at the scene, verifies and cross-checks the information gathered. It uses all techniques to materialize the facts.

In which cases does the forensic science department intervene?

The daily work of the forensic police of Poitiers is to intervene – in the order of the number of cases – on burglaries, robberies, discovery of stolen vehicles, corpses (found on the public highway, unidentified, suspicious deaths…), violence to persons, damages, fatal accidents, work accidents, rapes and drug trafficking.

In France in 2020, the police made 350 000 interventions and 50 000 identifications. In Poitiers, they made 2,000 trips and 250 identifications.
The forensic police look for material evidence following a very precise protocol. At the scene, they start by taking pictures to freeze the scene, look for traces and clues, install riders (these small numbers that identify the objects in the scene on the pictures) and take samples (objects, weapons).

The tools of forensic science

A number of samples are taken from a crime scene and from the suspect(s): fingerprints, hair, semen, gunshot residue on the shooting hand, presence of blood. To identify the presence of blood that is not visible to the naked eye, because the scene was cleaned before the police arrived, the forensic science team uses Bluestar to reveal the erased traces. The luminol makes the iron in the blood react.

The Poitiers crime lab is a pilot site in France for the digital forensics service.

Forensic medicine and DNA in the service of the truth

Forensic medicine is an essential tool of the scientific police. The autopsy is used to determine the circumstances of the death. Forensic scientists perform two types of examinations:

external examination of the body to determine ante-mortem and post-mortem trauma. The autopsy is an opening of the body to identify types of trauma, violence, blows, to take samples, to see the state of the lungs (in case of drowning) and to identify a body in bad condition, by taking a sample from the femur. The forensic pathologists will submit a forensic autopsy report.

DNA is a tool used on a daily basis by forensic scientists, including for burglaries. DNA is often a hope for cold cases, those cases that have remained unsolved for years (like the Grégory case or the Omar Raddad case). To be efficient, it is necessary to have a large quantity of quality samples and a good conservation of the seals, because the enemies of DNA are known: light, humidity, heat, UV rays…

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