Body Fluids Forensic Serology How is blood evidence

Body Fluids Forensic Serology

How is blood evidence detected at a crime scene? Light Source Investigators will first examine the crime scene to look for areas that may contain blood. They may use a high-intensity light or UV lights to help them find traces of blood as well as other bodily fluids that are not visible under normal lighting conditions. Blood Reagent Tests These tests, referred to as presumptive tests, are used to detect blood at crime scenes based upon the properties of hemoglobin in the blood. Further tests at the crime lab can determine if it is human blood or not. Examples: • Phenolphthalein is a chemical that is still utilized today and is usually referred to as the Kastle-Meyer test and produces a pink color when it reacts with hemoglobin. • Hema. Stix is a strip that has been coated with tetramethylbenzidine (TMB) and will produce a green or bluegreen color with the presence of hemoglobin. Hema. Stix

Luminol This chemical is used by crime scene investigators to locate traces of blood, even if it has been cleaned or removed. Investigators spray a luminol solution is throughout the area under investigation and look for reactions with the iron present in blood, which causes a blue luminescence. One problem is that other substances also react, such as some metals, paints, cleaning products, and plant materials. Another problem is that the chemical reaction can destroy other evidence in the crime scene. Fluorescein This chemical is also capable of detecting latent or old blood, similar to luminol. It is ideal for fine stains or smears found throughout a crime scene. After the solution has been sprayed onto the substance or area suspected to contain blood, a UV light and goggles are used to detect any illuminated areas, which appear greenish-white if blood is present. It may also react to many of the same things as luminol (copper and bleach). Luminol Reaction Fluorescein Reaction in UV Light LCV or Leuco Crystal Violet, is one type of chemical process that is used for blood enhancement. Using this test helps to make the blood evidence more visible so it can be photographed analyzed.

Bloodstain Pattern Analysis Terms Spatter – Bloodstains created from the application of force to the area where the blood originated. u Origin/Source – The place from where the blood spatter came from or originated. u Angle of Impact – The angle at which a blood droplet strikes a surface. • Parent Drop – The droplet from which a Satellite Spatters satellite spatter originates. • Satellite Spatters – Small drops of blood Spines that break of from the parent spatter when the blood droplet hits a surface. • Spines – The pointed edges of a stain that radiate out from the spatter; can help Parent Drop determine the direction from which the blood traveled. u

Types of Bloodstain Patterns u Passive Bloodstains – Patterns created from the force of gravity – Drop, series of drops, flow patterns, blood pools, etc. • Projected Bloodstains – Patterns that occur when a force is applied to the source of the blood – Includes low, medium, or high impact spatters, castoff, arterial spurting, expiratory blood blown out of the nose, mouth, or wound. • Transfer or Contact Bloodstains – These patterns are created when a wet, bloody object comes in contact with a target surface; may be used to identify an object or body part. – A wipe pattern is created from an object moving through a bloodstain, while a swipe pattern is created from an object leaving a bloodstain. Images from http: //www. bloodspatter. com/BPATutorial. htm

Microscopic Views Fish Blood Bird Blood Horse Blood Frog Blood Cat Blood Dog Blood Human Blood Snake Blood

The Precipitin Test When human blood is introduced to the animal’s antihuman antibodies it produces a clot called a precipitate clot. This precipitate clot can be formed in a test valve identifying whether or not a blood sample is human or not. This test is called the Precipitin Test. 1. Animal is injected with human blood 2. Animal makes anti-human antibodies 3. Animal blood is extracted 4. The extracted animal blood is used to test other blood to identify whether the blood is of human origin

Bloodstain Evidence May reveal: Origin(s) of bloodstain u Distance of bloodstain from target u Direction from which blood impacted u Speed with which blood left its source u Position of victim & assailant u Movement of victim & assailant u Number of blows/shots u

Liquid Blood u Physical properties 1. 2. 3. u Viscosity Surface tension Specific gravity (relative density) Behaves as a projectile in motion – Biology, physics, mathematics…

Surface Tension u u Resistance to penetration & separation Surface acts to reduce surface area u Smallest SA to Volume ratio is offered by sphere

Blood Drips 1. Blood trickles downwards 2. Blood drop grows until Wt (G) > S. T. Single drop breaks free (teardrop shape) 3. Surface tension pulls in vertically 4. And horizontally 5. Shape settles into sphere (0. 05 ml) Does not break up until impact https: //www. shutterstock. com/video/clip-3503306 -stock-footage-drop-of-blood -falling-from-syringe-on-white-background-in-slow-motion. html http: //www. gettyimages. com/detail/video/blood-droplets-falling-against-whitebackground-stock-video-footage/113482689

Drop size Rapid bleeding gives Standard drop size 50 ul (0. 05 ml) slightly larger drop Shaking/movement casts off smaller drops . . .

Free Falling Blood Droplets 0. 06 ul 1. 1 mm . 0. 5 to 0. 65 m 2. 2 m/s 0. 12 ul 1. 32 mm . 0. 5 ul 2. 12 mm 0. 84 to 1 m 3. 3 m/s . 2. 4 to 3 m 4. 6 m/s 50 ul 4. 6 mm 4. 2 to 5. 4 m . 7. 5 m/s

Shape & Size of Bloodspot u The size of a blood spot depends on distance fallen and surface type.

Shape & Size of Bloodspot u Depends mostly on nature of target surface – texture (rough or smooth) – porous or non porous u Size is related to distance fallen, provided: – standard 50 ul drop of blood u There is little change in spot diameter beyond a fall distance of 1. 2 m

Effect of Target Surface . Smooth Surface Spreads out smoothly . Rough Surface . . ST of spreading edge is broken by irregular surface

Single drop of blood falling from various heights (m) onto various surfaces 0. 5 1 1 Height/Surface 2 2 3 3 smooth floor paper towel fabric

Height Fallen Single drops of blood falling from fingertip onto smooth cardboard from various heights. No change in diameter beyond 7 ft. Adapted from Introduction to Forensic Sciences, W. Eckert, CRC, 1997

Experiments with Falling Blood Droplets blood Height dropper ruler Target Surface Fabric (theatre green) rough paper towel paper whiteboard Terazzo floor

Angle of Impact 90 60 80 50 70 40 Gravitational dense zone at lower edge 30 Adapted from Introduction to Forensic Sciences, W. Eckert, CRC, 1997 20 10

At 90°, blood stains will be almost circular. Below 75°, spines become more prominent on the side of the spatter opposite the angle of impact. At very low angles, a second, satellite spatter may break off, forming a distinctive “exclamation point” stain pattern.

Wave Cast-off Tail of elongated stain points in direction of travel . Tail of wave cast-off points back to parent drop Parent drop wave cast-off