PS08 - Crime Scene Investigation and Coordination
Forensic expert - Forensic Department "Anthropology and Hemato morphology", IRCGN
One of several specialities in the field of forensic science, involves the study and analysis of blood at a crime scene with the goal of helping investigators about bloody details of the scene. Blood can give informations about the « who » (DNA) and about the « how » (bloodstain pattern analysis). But we still do not have any way to answer about the « when » blood was deposited on the scene.
In 2012, the state of the art made by the PhD BREMMER and al (Forensic quest for age determination of bloodstains, Forensic Sci Int .2012 Mar 10;216(1-3):1-)11.) mentionned a list of methods trying aging blood. None were transposable on a scene of crime.
Trying to solve this problem, we proceed in a reverse order : which materials the CSI already have in their suitcases ? With it, which informations could we obtain ?
In 2012, we started a collaboration with the CNRS and obtained an ANR budget in 2014 (D-BLOOD N°ANR-13-BS09-0026-04, collaborators : IUSTI MARSEILLE, ENS PARIS, LRP GRENOBLE, NFI).
We started our study focusing on the drying process of blood pools to determine what relevant information can be obtained for the forensic application and for dating blood
Material : Double JACOMEX GLOVEBOX (700l)? balance METTLER TOLED ML802, NIKON D200 and D7000, lense 60 mm, testo A-G 175-52, GEM 4000 and COBAS INTEGRA 400 PLUS
Sample of whole human blood were deposited on tiles inside the double glovebox and all parameters were recorded (controlled shape and humidity, known temperature, volume, mass, composition of blood, in order to see the impact of those parameters on pools while drying)
First we found that the drying process can be separated into five different stages, visible to the naked eyes : coagulation, color change (possible gelation), rim dessication, center dessication and final dessication.
This rim dessication is always starting from the outline towards the center of the pool, but its speed is not constant.
Moreover, by normalizing the mass and drying time, we showed that the mass of blood pools was diminishing similarly and in a reproducible way for blood pools created under various conditions. Finally, mainly link between hygrometry and
blood drying is observered.
The results of all our experiments are used to create a substantial database.
A software is developed to automatized the study of the drying front speed and the database is used to start the creation of a software able for the prediction (machine learning) of the time of deposit for pool of blood on crime scene.
Otherwise, hardly any other links have emerged from our study, which is a goodpoint because it means our software can be used without detailed blood analysis. This software is still in progress because we would like to implement it with other parameters, but our first results are promising.
BPA, blood pools, dating,