Blood Evidence Collection and Analysis Notes

Biological (Blood) Evidence

Terminal Performance Objective:

  • Apply basic concepts and principles of blood collection necessary to obtain blood evidence suitable for forensic laboratory analysis and court proceedings.

Enabling Performance Objectives

  1. Identify methods for locating and confirming the presence of blood evidence.

  2. Identify concepts of bloodstain pattern analysis.

  3. Identify biological evidence hazards and demonstrate safe handling requirements.

  4. Identify and demonstrate proper collection and packaging of biological evidence.

EPO #1: Locating and Confirming Blood Evidence

  • Blood transports metabolic waste products away from cells.

  • Red Blood Cells:

    • Generated from bone marrow at a rate of 4-5 billion per hour.

  • Platelets:

  • Locating Blood Evidence:

    • Close visual examination is typically used to search for blood at a crime scene.

    • Tiny particles of blood can cling to most surfaces for years.

    • Even if a murderer disposes of the victim's body and cleans up pools of blood, some evidence will likely remain without heavy-duty cleaning chemicals.

  • Latent Bloodstains:

    • Cannot be seen with the naked eye.

    • Investigators use chemical reagents like Luminol or BlueStar to find and photograph them.

  • Luminol:

    • Reveals traces of blood through a chemiluminescent reaction.

    • Involves a light-producing chemical reaction between chemicals and hemoglobin (an oxygen-carrying protein in blood).

    • Chemiluminescence is the same phenomenon that makes fireflies and light sticks glow.

  • Bluestar:

    • Extreme sensitivity allows the naked eye to detect bloodstains down to 1:10,000 dilutions, even minute traces washed off with or without detergent.

    • Has a stronger and longer-lasting luminescence that doesn't require total darkness.

    • Investigators can use the luminescent reaction to locate potential blood evidence undetectable through visual examination.

    • The reaction is not specific to blood; other oxidizing agents like sodium hypochlorite (bleach), certain metals, and plant peroxidases may also cause luminescence with luminol.

  • Presumptive Blood Testing:

    • Phenolphthalein:

      • A positive reaction is indicative of blood, but it is only a presumptive test and false positives are possible.

      • Positive reactions are not limited to human blood.

    • Leucomalachite Green:

      • A chief metabolite of malachite green, a triphenylmethane dye that has been used generally as an antifungal drug in the fish industry

      • An immediate blue-green color change indicates a positive result

      • No color change indicates a negative result

  • Plasma:

    • The liquid portion of blood, yellowish in color, consisting mostly of water but also contains proteins, sugars, hormones, and salt.

    • White Blood Cells:

EPO #2: Bloodstain Pattern Analysis

  • Blood is the most common body fluid found at violent crime scenes and can provide valuable information.

  • Blood behaves according to scientific principles, allowing trained analysts to examine bloodstain patterns and draw conclusions about how the blood was shed.

  • Analysts categorize stains by gathering information from spattering patterns, transfers, voids, and other marks to help recreate the sequence of events after bloodshed.

  • Bloodstain pattern analysis requires analysts to recognize and interpret patterns to determine how they were created.

  • BPA uses principles of biology, physics, and mathematics.

  • Blood is in a liquid state when inside the body, and when it exits the body, it does so as a liquid.

    • Except for people with hemophilia, blood will begin to clot within a few minutes, forming a dark, shiny gel-like substance that grows more solid as time progresses.

    • The presence of blood clots in bloodstains can indicate that the attack was prolonged or that the victim was bleeding for some time after the injury occurred

  • Blood can leave the body in many different ways, depending on the type of injury inflicted

    • It can flow, drip, spray, spurt, gush or just ooze from wounds

3 Types of Bloodstains:

  • Passive stains

  • Transfer stains

  • Projected or Impact stains

Impact Spatter:

  • Created when a force is applied to a liquid blood source.

Projection Spatter:

  • Caused by arterial spurting, expiration spray, or spatter cast off an object.

  • Gunshot Spatter:

    • Includes both forward spatter from the exit wound and back spatter from the entrance wound.

    • Gunshot spatter will vary depending on the caliber of the gun, where the victim is struck, whether the bullet exits the body, the distance between the victim and the gun, and the location of the victim relative to walls, floors, and objects.

    • Typically, forward spatter is a fine mist, and back spatter is larger and has fewer drops

  • Cast-off:

    • Results when an object swings in an arc, flinging blood onto nearby surfaces.

    • Occurs when an assailant swings the bloodstained object back before inflicting another blow.

    • Analysts can tell the direction of the impacting object by the shape of the spatter (tails point in the direction of motion).

    • Counting the arcs can also show the minimum number of blows delivered

  • Arterial Spray:

    • Refers to the spurt of blood released when a major artery is severed.

    • The blood is propelled out of the breached blood vessel by the pumping of the heart and often forms an arcing pattern consisting of large, individual stains, with a new pattern created for each time the heart pumps

  • Expirated Spatter:

    • Small air bubbles in the drops of blood are typically found in this type of spatter

    • Usually caused by blood from an internal injury mixing with air from the lungs being expelled through the nose, mouth, or an injury to the airways or lungs.

  • Sharp force injuries (stabbing):

    • These injuries are caused by an object with a relatively small surface area, such as an ice pick or a knife.

    • Less blood is deposited on the instrument, resulting in a smaller, more linear pattern of stains.

  • Blunt force injuries (hitting or beating):

    • Objects inflicting this type of injury are usually larger, such as a bat or hammer.

    • If the object impacts liquid blood, the larger surface area will collect more blood, producing drops of varying sizes

  • When blood is impacted, droplets are dispersed through the air.

  • As the angle of impact decreases, the spatter stain elongates, becoming more elliptical, and the spines, etc., become more predominant opposite the angle of impact.

  • Void:

    • Occurs when a person or object blocks the path of the blood.

    • They are important because voids can show investigators if objects are missing from the scene, where a person was at the time of the incident and if a body was moved

    • An object that leaves a void in a bloodstain pattern will have a matching bloodstain pattern on its surface, allowing analysts to replace it in the scene if found

  • Analyzing bloodstains helps investigators answer basic questions:

    • What occurred?

    • Where did the events occur?

    • Who was there?

    • Where were they in relation to each other?

    • Approx. when and in what sequence?

  • How bloodstain evidence is collected:

    • Bloodstain samples can be collected for BPA by cutting away stained surfaces or materials, photographing the stains, and drying and packaging-stained objects

    • The tools for collecting bloodstain evidence usually include high-quality cameras (still and video), sketching materials, cutting instruments, and evidence packaging

    • A scale or ruler is placed next to the bloodstain to provide accurate measurement, and photos are taken from every angle

  • Documentation of Bloodstain Evidence:

    • Before a crime scene investigator begins documenting and collecting blood evidence, they must recognize the value of this evidence and how it fits in the overall events associated with the crime.

    • The most common applications of blood evidence are:

      • Finding blood with the victim’s genetic markers (ABO blood type, DNA profile, etc.) on the suspect, on something in the suspect’s possession, or something associated with the suspect (such as the suspect’s fingerprints).

      • Finding blood with the suspect’s genetic markers on the victim, on something in the victims possession, or on something associated with the victim

    • Since blood evidence associated with a crime can provide information that may solve the case, it is essential to correctly document, collect, and preserve this type of evidence

    • Improperly handled blood evidence can weaken or destroy a potential source of facts in a case

  • In the 1990s, most crime labs were relying on DNA analysis to characterize bloodstains

    • This meant that the blood could have come from 4 to 49% of the population

    • A blood source can now be statistically narrowed down to one person out of several million or even several billion

  • Generally, blood evidence is usually more informative in cases where a suspect and victim are in contact or close proximity. For example:

EPO #3: Biological Evidence Hazards

  • Contact with bodily fluids can spread diseases caused by bloodborne pathogens, so individuals handling biological evidence should treat it as hazardous to ensure safety.

  • Individuals handling any biological evidence should assume that all of it may contain potentially hazardous biological material.

  • Examples of biological evidence hazards:

    • Hepatitis can live for years in the open air; the virus was shown to still be alive even after hepatitis-contaminated evidence had been frozen and thawed years later.

    • AIDS can survive for up to 4 weeks in a used syringe.

    • MRSA (a potentially deadly flesh-eating staphylococcus) can live outside a person’s body for multiple months.

  • Universal precautions:

    • The U.S. Occupational Safety and Health Administration (OSHA) developed universal precautions to protect workers from exposure to human blood or other potentially infectious materials.

    • When individuals handle any type of biological evidence, procedures need to be in place to reduce or eliminate the risk of exposure to bloodborne pathogens that can transmit disease (OSHA 2012)

  • Personal Protective Equipment (PPE):

    • The appropriate use of PPE is intended to protect the individual and the evidence from cross-contamination.

    • PPE includes disposable nitrile gloves, disposable overalls, laboratory coats, face protectors, splash goggles, or other eye protection

    • PPE such as head and hair covering, foot coverings, and a protective suit with a hood may be required, depending on the specific situation, for individual safety and to avoid contamination of the evidence

    • PPE must be clean and in good repair

    • PPE should be used in every situation in which there is a possibility of exposure to blood or infectious diseases

    • Gloves and protective clothing should be worn when Providing first aid or medical care, handling soiled Materials or equipment, and cleaning crime scenes

    • PPE that is torn or punctured or that has lost its ability to function as an effective barrier should not be used

    • While using PPE, individuals should not touch their eyes or nose with gloves

    • Used protective clothing and equipment must be placed in designated areas for storage, decontamination, and disposal

    • PPE must be removed when it becomes contaminated and before leaving the work area

    • Dried blood or other dry, potentially infectious material should not be assumed to be safe

  • U.S. Occupational Safety and Health Administration (OSHA) makes guidelines for what precautions to use when there is potential exposure to human blood or other potentially infectious materials.

EPO #4: Proper Collection and Packaging of Blood

  • Extreme care must be taken to avoid contamination.

    • Never transport victims and suspects together.

    • Avoid talking, sneezing, and coughing over evidence.

    • Don’t touch the face, nose, head, and mouth when collecting evidence

  • Biological evidence that is found during an LE investigation needs to be evaluated, collected, and preserved to ensure the evidence is not degraded or contaminated

  • Consideration must be made for any forensic materials on the object, such as fingerprints or blood

    • Avoid contact between items

    • If blood is on the object, then it must be allowed to air dry and then wrapped in a clean piece of paper and properly sealed before placing it in the final container

    • Whenever possible, the entire object containing the biological evidence (aka the whole holder of evidence) should be collected

    • This method is not typically feasible for large items of furniture, structures, or other extremely large items

  • Swabs:

    • There are many instances where investigators may need to take samples using swabs. They are easy to use, individually packaged, sterile, handy, and relatively cheap

    • Blood, Biological, and Trace evidence is required to be “double packaged”

    • When dealing with swabs, use the theory of “One Is None, and Two Is One”

      • For each collection, you will use two sterile swabs

      • The first swab will remain in its original state as your “control.”

      • The second swab will contain your “sample.”

        • You will obtain your sample by placing the tip of the swab in the middle of the stain and wetting the tip. It is not necessary to soak the swab

    • Some versions have large holes in the sides of the small container that allows air to circulate freely

      • These holes are also used to hold the non-sterile end of the item and allow the wet sample to air dry

      • Then place the items into the evidence container or envelope. (Note: This will be one item on the 3524, but quantity two since two swabs (Sample and Control) are attached in the same evidence package

  • Before packaging any biological evidence, it is important to airdry the evidence thoroughly