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Blood residue are the wet and dry remnants of blood, as well the discoloration of surfaces on which blood has been shed. In forensic science, blood residue can help investigators identify weapons, reconstruct a criminal action, and link suspects to the crime. In archaeology, it can be used to detect of origin of blood stains on buried objects.
Laboratory testing can reveal whether a substance is indeed blood, whether the blood is of animal or human origin, and the blood group to which it belongs. This allows investigators to include or exclude persons as perpetrators or victims. The antigens that allow blood group testing, however, deteriorate with age or improper storage.Robinson, 154. The DNA contained in blood, on the other hand, is less subject to deterioration, and allows near-certain matching of blood residue to individuals with DNA profiling techniques. Through bloodstain pattern analysis, information about events can also be gained from the spatial distribution of bloodstains.
Crime scenes are normally carefully searched for blood residue. Flashlights held at an angle to the surfaces under examination assist in this, as do luminol sprays which can detect even trace amounts of blood. Presumptive tests exist with which blood can be distinguished from other reddish stains, such as of ketchup or rust, found at the scene. The search includes areas beyond the immediate crime scene where blood might have been wiped off or bloody fingerprints left, such as towels or doorknobs. At outdoor crime scenes, bloodstains may be recovered from the ground or from plant surfaces.Robinson, 153.
The standard documentation of blood residue includes photographs and descriptions of form, color, size and position of each stain found. Overall photographs and sketches are also produced to show the relationship of the blood residue to other elements of the scene and to enable pattern analysis. Recently 3D imaging techniques have been tried for documenting and investigating bloodstains.
Haemotaphonomy has also been used to study blood residues on fragments of medieval manuscripts, and on the Shroud of Turin.
The term haemotaphonomy was proposed in 1992. It was inspired by the word "taphonomy" introduced in Paleontology in 1940 by Ivan Yefremov. The focus of haemotaphonomy is the morphology of blood cells when blood is in the form of a stain. Therefore, its subjects of study are any specimens stained with blood. The study method of haemotaphonomy is the analysis of images obtained through a scanning electron microscope (SEM). However, confocal microscopy is a practical alternative to an SEM when a very high level of detail of the bloodstain surface is not required.
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