Blood Stain Evidence

2. Blood Stain Evidence • Blood is a type of biological evidence that can connect a suspect to a victim or object. • White blood cells contain DNA which may be used to identify an individual from a blood sample. • Lab testing can differentiate between human and animal blood by protein or DNA analysis.

3. Biological Properties of Blood • Blood delivers nutrients and oxygen to the cells and transports waste products away from cells. • Red blood cells carry oxygen and carbon dioxide.

4. Biological Properties of Blood • White blood cells come in many varieties that fight off infection in different ways, such as by generating antibodies or breaking down intruder cells. • They also contain DNA.

5. Biological Properties of Blood • Platelets assist in clotting.

7. Biological Properties of Blood • Main elements used in forensic labs: • Red blood cells • Serum proteins • Red blood cells have structures called antigens on their surfaces. They are grouped into classification systems determined by their relationship to one another (blood type).

8. Biological Properties of Blood • Serum proteins such as antibodies are used to test the sample to confirm that it is blood. • An antibody activates or destroys a specific antigen which allows for particular reactions to occur when specific groups of antigens and antibodies are mixed. • These reactions allow for determination of blood type.

9. Biological Properties of Blood • The ABO group system for blood typing was first used in the early 1970’s to link blood to an individual. • An individual that is type A has A antigens on their red blood cells. • Type B has B antigens on their red blood cells. • Type AB has both A and B antigens. • Type O has neither A or B antigens.

10. Biological Properties of Blood • In addition to the A and B antigens there is also another antigen, the Rh factor. • Its presence is indicated by a positive sign and its absence is indicated by a negative sign. • This is appended after the A/B/O indicator.

11. Blood Type Frequency

12. Blood Origin Testing • Two categories of tests are available for investigators. • Presumptive tests are used to quickly determine whether an unknown substance is blood in the field. They are prone to false positives. • Confirmatory tests must be done at a lab and provide much more accurate results.

13. Blood Origin Testing • Two categories of presumptive tests are: • Color changing tests • Luminol, Benzidine, Phenolphtalein, TMB / Hemastix • Glowing reaction tests • fluorescein

14. Phenolphthalein Presumptive Test • This test is better known as the Kastle-Meyer test. • In a positive reaction the reduced phenolphthalein will turn bright pink because the phenolphthalein is oxidized by hydrogen peroxide in the presence of hemoglobin. • Phenolphthalein reagents give false positives when vegetable materials are present.

15. TMB / Hemastix Presumptive Test • This test is performed with commercial plastic strips with a treated filter at one end. • A test swab is moistened with water and placed in contact with the stain. The swab is then placed onto the tip of the strip. • If blood is present the hemastix strip will turn green.

16. Luminol Presumptive Test • Luminol tests for latent bloodstains. It can detect blood that has been diluted up to 1 in 10,000,000. • When luminol and hydrogen peroxide are applied to the bloodstain the luminol produces a blue-white to yellow-green light. • Luminol can affect some testing processes but does not affect most blood typing or DNA analysis. • It produces a false positive with plant enzymes, oxidizers, metals, and chlorine.

17. Fluorescein Presumptive Test • Fluorescein tests for latent bloodstains by fluorescing under ultraviolet light. • It can even detect blood stains that have been cleaned with solvents such as bleach. • Fluorescein can also be applied to vertical surfaces, unlike luminol. • Copper and hypochlorite will cause false positives.

18. Presumptive Test Summary

19. Blood Origin Testing • Once a stain has been characterized as blood through a presumptive test it is collected and stored for confirmatorytesting. • The two most common confirmatory tests are the Takayama and Trichmann tests.

20. Takayama Confirmatory Test • The Takayama test is performed by adding an alkaline solution with a specific structure of hemoglobin to the stain on a microscope slide. • If blood is present, pink crystals will be observed as the slide is heated.

21. Trichmann Confirmatory Test • The Trichmann test is performed by adding a small amount of chloride containing acetic acid to the blood sample on a microscope slide. • Small crystals form on the slide as it is heated if blood is present. • Once the stain is confirmed as blood, it must be tested to determine if the source is human or animal.

22. Blood Origin Testing • The precipitin test will determine whether the stain is of human or animal origin. • The precipitin test uses an antigen that is designed to destroy human blood. • This test takes advantage of the fact that antigens and antibodies naturally move toward each other on a gel plate. • The extracted blood stain (antigen) and the human antiserum (antibody) are placed in separate holes opposite each other on the gel. If the blood is human, a line of precipitation forms where the antigens and antibodies meet.

23. Blood Properties • Since the 1990’s DNA found in the blood and other bodily fluids has been used to identify an individual, like a genetic fingerprint.

24. Blood Properties • DNA is unique to the individual, whereas blood typing can only eliminate an individual as a suspect. Blood type is class evidence and DNA is individual evidence. • The process of genetic fingerprinting is called DNA profiling or DNA typing.

25. Evidence Handling • It is crucial that bloodstains found at a crime scene are documented, collected, tested, preserved, and analyzed correctly. • Failure to do so will weaken or destroy potential evidence.

26. Evidence Handling • Proper evidence packaging is crucial to protect against: • Loss • Contamination • Deterioration • Cross-transfer • Suspect / scene / item / victim • Biohazards

27. Evidence Labeling • Labeling • Evidence description • Source (location, agency) • Chain of custody • Case and item numbers • Health hazards • Storage conditions (room temp, frozen, refrigerated)

28. Evidence Labeling • Biological material must be dried before packaging to prevent deterioration. • Dry at room temperature, do not use a heat gun, fan, or hair dryer. • Use paper containers for biological evidence. • Seal evidence with tape across the bag, initial and date over or under seal.

29. Evidence Packaging • Work on clean surfaces. Wear gloves, a mask, and eye protection – don’t contaminate with DNA. • Change gloves after handling each sample to eliminate cross-contamination. • Do not blow on samples to make them dry faster. • Do not touch blood samples with any non-disposable items. • Clean tools with 10% bleach solution and dry thoroughly.

30. Evidence Packaging • Keep all stains separated. • Separate stains on the same garment with sheets of paper. • Package multiple garments in different bags. • Do not use any packaging that limits air exposure (tubes, parafilm, plastic baggies)

31. Evidence Storage • Biological evidence should be stored dry to prevent bacteria or mold growth. • Wet evidence should be stored frozen. • Some portion of samples should be preserved from destructive testing.