A team of scientists from the University of Valencia (UV) has proven that traces of blood in various materials are eliminated completely when they are washed with detergents containing active oxygen. The conclusion of the study, published in the latest number of the German journal entitled Naturwissenschaften, points out that these new products alter blood to such an extent that this cannot be detected by reagents used in forensics.
The intention of the authors of a crime is not to leave any proof that can link them to the crime and often they clean the scene of the crime or wash their clothes in order to eliminate any signs that may give them away. However, until now police scientists have been able to discover the traces of blood thanks to reagents such as luminol, phenophthalene or the human haemoglobin test, but the new detergents are making this more and more difficult to achieve.
A study undertaken by scientists from the UV and published this month in the journal entitled Naturwissenschaften, has shown that if materials stained with blood are washed with products containing active oxygen, the luminol, phenophthalene and human haemoglobin tests give a negative result.
"The impossibility of locating these traces means that very important evidence such as DNA profiles obtained from blood is lost" Ana Castelló tells SINC, and who is one of the authors of the study and a lecturer in Legal and Forensic Medicine at the University of Valencia.
The researcher explains that the experiment they carried out involved placing several drops of blood onto three types of material, namely white cotton, a pair of jeans and a towel and letting these dry for different lengths of time, namely one, five, ten, twenty, thirty and forty days respectively. The samples were then taken and washed using a product containing active oxygen.
"Regardless of the type of material used and the time that had elapsed, in every single case where the three tests were performed, the presence of blood was not detected, points out the researcher. Generally, in the crime scene, phenophthalene orientation tests are used first (these turn bright pink in the presence of oxygenated water and blood or other substances) followed by luminol, which illuminates traces of blood in the dark, and lastly the human haemoglobin test is performed in order to confirm the presence of blood.
Although the researchers had proven that the results were negative in those samples that were one day old, they considered it appropriate to study traces of up to 40 days old because luminol is more effective on old stains than recent ones. However, they did not obtain positive results, even by doing this.
An unresolved mystery
The scientists have not yet determined the cause whereby active oxygen interferes in blood detection methods, but the authors have suggested a hypothesis. Castelló speculates that "the active oxygen products contain sodium percarbonate, and when this is dissolved in water, a considerable quantity of hydrogen peroxide (oxygenated water) is released, and it is possible that the inhibitory effect may be due to the "depletion" of haemoglobin in the attempt to eliminate the peroxide".
Even so, the researcher concludes that washing the materials with products containing active oxygen does not eliminate the blood completely because brown traces remain, but it certainly does prevent detection by means of current tests, "and it is advisable to take account of this when using these methods in criminalistic research".
The lecturer in Legal Medicine recognises that this poses a "serious" problem to the police scientists and insists that if the blood is not located DNA cannot be extracted from fluid, such that important evidence is lost in the resolution of certain crimes. However, Castelló, has advised SINC that they are now working on new markers in order to help resolve this situation.
- Castelló et al. Active oxygen doctors the evidence. Naturwissenschaften, 2009; 96 (2): 303 DOI: 10.1007/s00114-008-0466-9
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