Análisis químico-forense de patrones hemáticos en relación a la superficie de soporte en manchas sanguíneas

Abstract

In the forensic sciences, the application of reconstructive and identifying hematology is fundamental, since, at a crime scene, blood samples are analyzed within the laboratory, to recognize their origin. Reconstructive hematology determines the angle, distance and dynamics used during the commission of a crime and these stains are called blood patterns, which are classified into different types. The analysis of stains found at a crime scene is carried out through techniques of guidance and certainty, which indicate if it is a biological fluid and in turn if it is human blood. Among the orientation techniques we have benzidine, phenolphthalein, leuco malaquita and luminol, these are manual techniques that have been applied for a long time, as well as certainty techniques such as Teichman, Takayama and microscopy require manual procedures. Currently, more advanced technologies such as Raman, NIR and Scanning Electron Microscopy are presented that are applicable according to different cases in forensic investigations, where factors such as the age of the blood stains intervene. In this work, blood patterns were analyzed on 5 surfaces at 5 different heights by static dripping. In addition, a follow-up for 4 weeks to the change of stain coloration through photographs and a comparative microscopic analysis between the human and animal blood forms. Blood stains acquire different qualities, and this will vary in their morphology according to the characteristics presented by each surface depending on external aspects such as speed, strength of attack, angle and height. The time in which the blood is exposed to the external environment will modify its characteristic color according to the weeks of exposure, since it can change from a brown, red color to a dark brown color. Human blood (mammalian) and animal blood (oviparous) present differences between the shape and nucleus of their erythrocytes and when analyzed under histological techniques; erythrocytes of human blood are observed with a circular and absent form of nucleus, whereas, in animal blood, erythrocytes with elongated shape and nuclei are observed. The characteristics of the static drip blood patterns were interpreted based on the support on which it falls and how these changed the morphology of the blood stains at higher altitudes. The color change of the blood stains was determined during the first hours and later after 4 weeks that the stains were exposed on the different surfaces. The comparison of the shape elements of human and animal blood was carried out through a microscopic analysis, where the differences between the characteristics of the erythrocytes (nucleus and shape) were analyzed. When performing the histological identification technique, better results will be observed with fresh blood samples using the microscope.