Blood residue
Encyclopedia
In forensic science, blood residue – wet and dry remnants of blood
, as well the discoloration of surfaces on which blood has been shed – can help investigators identify weapons, reconstruct a criminal action, and link suspects to the crime. Blood residue analysis is also an important technique in archeology.
to the body, therefore, results in the shedding of blood. Its red color makes it readily apparent at crime scenes, and its residues are very difficult to completely remove. Blood residue has even been recovered from 100,000-year-old stone tools.
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. 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.
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.
, or collected with absorbent fabric that is allowed to air-dry. Dried blood is scraped off with a blade, or collected with a moistened cotton-tipped applicator, a gel lifter or fingerprint tape. Bloodstained clothing and other items are generally wrapped in paper and shipped whole to the laboratory. To prevent deterioration, blood residue samples are stored under refrigeration and, in the case of stains, air-dried.
Blood
Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....
, as well the discoloration of surfaces on which blood has been shed – can help investigators identify weapons, reconstruct a criminal action, and link suspects to the crime. Blood residue analysis is also an important technique in archeology.
Forensic significance
Blood constitutes about eight percent of a person's weight (normally about five liters), and it circulates near the surface of the skin. Almost all traumaPhysical trauma
Trauma refers to "a body wound or shock produced by sudden physical injury, as from violence or accident." It can also be described as "a physical wound or injury, such as a fracture or blow." Major trauma can result in secondary complications such as circulatory shock, respiratory failure and death...
to the body, therefore, results in the shedding of blood. Its red color makes it readily apparent at crime scenes, and its residues are very difficult to completely remove. Blood residue has even been recovered from 100,000-year-old stone tools.
Laboratory testing can reveal whether a substance is indeed blood, whether the blood is of animal or human origin, and the blood group
Human blood group systems
The International Society of Blood Transfusion currently recognises 30 major blood group systems . Thus, in addition to the ABO antigens and Rhesus antigens, many other antigens are expressed on the red blood cell surface membrane...
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. The DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
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
Bloodstain pattern analysis
Bloodstain pattern analysis is one of several specialties in the field of forensic science. The use of bloodstains as evidence is not new; however, the application of modern science has brought it to a higher level...
, information about events can also be gained from the spatial distribution of bloodstains.
Finding and documenting blood residue
Freshly dried bloodstains are a glossy reddish-brown in color. Under the influence of sunlight, the weather or removal attempts, the color eventually disappears and the stain turns gray. The surface on which it is found may also influence the stain's color.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
Luminol
Luminol is a versatile chemical that exhibits chemiluminescence, with a striking blue glow, when mixed with an appropriate oxidizing agent...
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.
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.
Collection and preservation
To collect samples for analysis, wet blood is collected with a syringe and stored in a tube with anticoagulantAnticoagulant
An anticoagulant is a substance that prevents coagulation of blood. A group of pharmaceuticals called anticoagulants can be used in vivo as a medication for thrombotic disorders. Some anticoagulants are used in medical equipment, such as test tubes, blood transfusion bags, and renal dialysis...
, or collected with absorbent fabric that is allowed to air-dry. Dried blood is scraped off with a blade, or collected with a moistened cotton-tipped applicator, a gel lifter or fingerprint tape. Bloodstained clothing and other items are generally wrapped in paper and shipped whole to the laboratory. To prevent deterioration, blood residue samples are stored under refrigeration and, in the case of stains, air-dried.