Serology Blood stain patterns Stain patterns of blood

Serology Blood stain patterns

Stain patterns of blood • The location, distribution, and appearance of bloodstains and spatters may be useful for interpreting and reconstructing the event that occurred to produce the bleeding.

Stain patterns of blood • When a blood stain is present, a complex and thorough analysis of the blood stain position and shape of blood patterns with respect to the origin and trajectory is completed.

Stain patterns of blood • Investigators seek to trace the direction, dropping distance and angle of impact of a blood stain.

Stain patterns of blood • When investigating surface texture of blood, the harder and less porous the surface, the less spatter results.

Textured surface Plastic Wall tile- non-texured

Assignment Page Stain patterns of blood • One can determine the direction of travel of blood striking an object. The pointed end of a bloodstain always faces its direction of travel.

Stain patterns of blood • It is possible to determine the impact angle of blood on a flat surface by measuring the degree of circular distortion of the stain. A drop of blood striking a surface at right angles gives rise to a nearly circular stain: as the angle decreases, the stain becomes elongated in shape.

Angle of Impact

Stain patterns of blood • The origin of a blood spatter in a two – dimensional configuration can be established by drawing straight lines through the long axis of several individual blood stains. The intersection or point of convergence of the lines represents the point from which the blood came from.

Point of convergence

Different types of splatter

Blood at the scene

Lack of splatter • The lack of splatter can also indicate what might have happened at a crime scene. • A person holding a weapon, should not have splatter where the weapon was.

Forensic Characterization of Semen • Many cases in forensic laboratories involve sexual offenses, making it necessary to examine for the presence of seminal stains. • The normal male releases 2. 5 to 6 milliliters of seminal fluid during an ejaculation. Each milliliter contains 100 million or more spermatozoa (the male reproductive cells).

Forensic Characterization of Semen • Forensic examination of seminal fluid is a two part process. • First step: the stain must be located. • Second step: determine the origin of the seminal fluid. • Many tests can be done to the fluid once it has been located (it may even be tested for the blood type of the individual from whom it originated).

Forensic Characterization of Semen • To help locate and characterize a seminal stain, an acid phosphatase color test can be done. • Acid phosphatase is an enzyme that is secreted by the prostate gland into seminal fluid.

Forensic Characterization of Semen • The acid phosphatase test can be done by adding sodium alpha naphthylphosphate and Fast Blue B dye to a suspected area. If the area turns purple, semen is present.

Forensic Characterization of Semen • Another test for semen is to use: 4 methylumbelliferyl phosphate (MUP). The garment in question can be pressed against a sizable piece of filter paper that has been sprayed with MUP, a UV light is then used, and any places that fluoresce under the UV light, will give a positive test for seminal fluid.

Forensic Characterization of Semen • The presence of semen can then be done utilizing a protein called p 30 or prostate specific antigen (PSA). • p 30 is unique to seminal plasma. • p 30 is injected into a rabbit, and the rabbit creates antibodies against it (similar to the precipitin test). The serum is collected and a gel diffusion is completed. If the liquids diffuse (move together), then the suspected stain proves that the stain was seminal fluid.

Forensic Characterization of Semen • Once seminal fluid has been identified, it must be looked at under the microscope for the identification of spermatozoa.

Forensic Characterization of Semen • There are instances where no spermatozoa are found in suspected seminal fluid. • There are men who have low sperm count (oligospermia) or have no spermatozoa (aspermia). This can be due to the rising number of vasectomies.

Forensic Characterization of Semen • Once the material under examination is proven to be semen, the next endeavor is to associate the semen to a single individual. • The link between semen and a single individual is done utilizing DNA technologies.