Forensic Serology & Blood Splatter Analysis Courtesy of C. Fanning

Unit Objectives for Serology Understand the physics of how blood splatter analysis can aid the forensics investigator in solving the crime. List and describe forensic tests used to characterize a stain as blood. Describe the proper collection of physical evidence in a rape case.

Forensics of Blood The criminalist must be prepared to answer the following questions when examining dried blood: 1. Is it blood? 2. From what species did the blood originate? 3. If the blood is of human origin, how closely can it be associated to a particular individual? The determination of blood is best made by means of a preliminary color test.

Testing for Blood A positive result from the Kastle-Meyer color test is highly indicative of blood. Hemoglobin causes a deep pink color. Alternatively, the Luminol test is used to search out trace amounts of blood located at crime scenes. Luminol produces light (luminescence) in a darkened area. Courtesy of C. Fanning Courtesy of C. Fanning Courtesy of C. Fanning

Testing for Seminal Stains Many of the cases sent to a forensic laboratory involve sexual offenses making it necessary to examine exhibits for the presence of seminal stains. Seminal stain are identified by acid phosphatase (an enzyme secreted into seminal fluid) color test. A purple color indicates acid phosphatase enzyme that indicates sperm

Rape Evidence 1. The rape victim must undergo a medical examination as soon as possible after the assault. At that time the appropriate items of physical evidence including.. clothing, hairs, and vaginal and rectal swabs All outer and undergarments should be carefully removed and packaged separately in paper (not plastic) bags. Bedding, or the object upon which the assault took place, may also be carefully collected.

Rape Evidence Within 24 hours of the assault, it may be possible to detect the victim’s DNA on the male’s underwear or on a penile swab of the suspect. Items routinely collected from the suspect include… all clothing, pubic hair, head hair, penile swab, and a blood sample or buccal swab for DNA typing.

What Happened? Crime-scene reconstruction relies on the combined efforts of … medical examiners Criminalists Law enforcement personnel to recover physical evidence and to sort out the events surrounding the occurrence of a crime.

Stain Patterns of Blood The crime scene investigator must remember that the location, distribution, and appearance of bloodstains and spatters may be useful for interpreting and reconstructing the events that produced the bleeding.

Document the Crime Scene You will need to document the crime scene to allow for later reconstruction to let the evidence tell the story of what happened. You document the scene with: Photos/ video Drawings Notes of observations

Blood Stains Tell a Story What 6 pieces of information could one deduce from the bloodstain pattern at a crime scene? direction of blood origin, angle the blood struck a surface, location of a victim, movement of a bleeding individual, minimum number of blows on the victim approximate location of the one delivering the blows

Blood Fall Height . What does the initial height of the blood drop do to the pattern of blood drops? the higher the drop, the bigger the velocity and the larger the diameter.

Angled Impacts The impact angle of blood on a flat surface can be determined by measuring the degree of circular distortion. At right angles the blood drop is circular, as the angle decreases, the stain becomes elongated.

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 bloodstains. The intersection or point of convergence of the lines represents the origin point.

Blood Spatter Blood drops form different shapes and sizes Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene.

Blood drops fall as small spheres Blood Spatter > Distance Determining Distance Blood Falls Blood drops fall as small spheres Drops form circle when hitting surface Size depends on speed of blood drop

Determining Distance Blood Falls Blood Spatter > Distance Determining Distance Blood Falls Faster drop = larger diameter (size) Higher distance = larger diameter Due to air resistance, speed maxes out at distances above about 7 feet

Determining Distance Blood Falls Blood Spatter > Distance Determining Distance Blood Falls However, size of drop also depends on the volume of the drop. Volume depends on the object blood originated from Example.. needle = small baseball bat = large

Determining Distance Blood Falls Blood Spatter > Distance Determining Distance Blood Falls Since the volume of blood is unknown… The distance a drop has fallen cannot be measured. Due to blood viscosity falling rate terminal velocity secondary spatterings.

Effect of Surface Smooth surface = smooth sphere Blood Spatter Effect of Surface Smooth surface = smooth sphere Rough surface may cause some splatter

Determining Direction of Blood Blood Spatter > Direction Determining Direction of Blood Narrow end of a blood drop will point in the direction of travel.

Determining Direction of Blood Blood Spatter > Direction Determining Direction of Blood If more than one drop (from spatter) results, the point of origin can be determined

Determining Direction of Blood Blood Spatter > Direction Determining Direction of Blood This is a 2-dimensional point of origin. It is possible to determine the 3-D point of origin

Determining Direction of Blood Blood Spatter > Direction Determining Direction of Blood The angle can be determined mathematically. Width/Length, then take the inverse sin (sin-1). This number is the impact angle (90 = perpendicular to surface; <10 at a sharp angle)

Blood Spatter > Direction For each blood drop, a string can be guided back to the point of origin.

Blood Spatter Types of Spatter Spattered Blood = random distribution of bloodstains that vary in size Amount of blood and amount of force affect the size of blood spatter. Can result from gunshot, stabbing, beating Help determine the location of the origin of the blood source. Help determine the mechanism which created the pattern.

Blood Spatter Spattered Blood In general, for higher impacts, the pattern is more spread out and the individual stains are smaller. Low impact = beating High impact = gunshot

Blood Spatter Types of Spatter Gunshot Spatter = can result in a mist-like spatter that indicates a gunshot. Not all gunshots will result in misting. Misting is the spray of small droplets. If misting is present, it is most likely a gunshot. Gunshots result in back spatter (where bullet enters) and forward spatter (where bullet exits).

Gunshot Splatter

Blood Spatter Types of Spatter Beating and Stabbing Spatter = larger individual stains First blow usually doesn’t result in spatter since there is not yet any exposed blood.

These drips are usually much larger than impact spatter. Blood Spatter Satellite Spatter = free falling drops of blood that fall onto a spatter pattern. These drips are usually much larger than impact spatter. However, blood dripping into blood can create a spatter.

Castoff Pattern = Blood flung off of swinging object. Blood Spatter Castoff Pattern = Blood flung off of swinging object. Can reconstruct where assailant and victim were positioned.

Can appear like beating or gunshot pattern. Blood Spatter Expirated Bloodstain Pattern = Blood can accumulate in lungs, sinuses, and airway. Forcibly exhaled. (caused from internal bleeding) Can appear like beating or gunshot pattern. May be mixed with saliva or nasal secretions.

A Void Pattern created when an object blocks the deposition of blood spatter onto a target surface or object.

Transfer and Contact Patterns When an object with blood on it touches one that does not have blood on it, this produces a contact or transfer pattern. Examples of transfers with features include… fingerprints, handprints, footprints, footwear prints, tool prints, and fabric prints in blood.

Trail Pattern of Bloodstains a series of drops that are separate from other patterns, formed by blood dripping off an object or injury

Arterial Spray Pattern created when a victim suffers an injury to a main artery or the heart. Commonly, the pattern shows large spurted stains for each time the heart pumps.

Alteration of bloodstain over time Blood Spatter Alteration of bloodstain over time Blood dries and clots over time. Difficult to estimate the time the blood exited the body. Clotted smears can indicate time of movement.

Bloodstain Patterns Physical Evidence Usually Found at Violent Crime Scenes Gives Clues as to WHAT Happened May Suggest Sequence of Events Analysis MUST be placed in context of all aspects of crime scene investigation in order to reconstruct (possible) criminal events.

Different Types of Bloodstain Patterns Passive Bloodstains (drops, pools, etc.) Transfer Bloodstains (wipe a weapon, etc.) Active (or “Projected”) Bloodstains (bullets, stepping in blood, etc.)

Active (or “Projected”) Bloodstains Rule of Thumb: As impact angle goes down, bloodstain shape becomes more elongated.

Active (or “Projected”) Bloodstains Impact Spatter – Blood source is “smacked” in some way and drops fly off in various directions. Divide category further by blood’s impact speed.

Low Velocity Velocity ≤ 5 ft/s stain size is (relatively) large: diameter ≥ 4mm examples: blood drops into blood and footstep spatters

Medium Velocity 5 ft/s ≤ velocity ≤ 25 ft/s stain size : 1 mm ≤ diameter ≤ 4mm examples: blood flicked off finger and blunt object used on victim

High Velocity velocity ≥ 100 ft/s ( 68 mph) stain size (relatively small): diameter ≤ 1mm examples: gunshots and propellers

sin θ = W / L W L What does W = L mean? sin θ = 1 → θ = 90 Drop is a circle!

Big Problem!!! Neither blood nor anything else travels unaided in a straight line through the air! Due to gravity, it travels in a Parabola as any projectile.

What about gravity???

What about air resistance??? (Drop’s speed and size are needed. Tough to know!) What about gravity???

Moral of the Story Calculation using “straight-line” trajectory (no gravity and no air resistance) predicts a “launch” point higher than actual point. “More accuracy requires a better model and more specialized work.