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Blood stains

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Blood stains

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  1. Blood stains

  2. Collection/Preservation of Blood Evidence • Secure scene • Alert EMT/Medical personnel to preserve clothing (e.g. bullet holes, knife holes in clothing) • Photograph bloodstains/document before removing stains • Maintain Chain of Custody – who has handled the evidence

  3. Blood Evidence • To collect blood from a movable item • Keep on item (if small – e.g. clothes, money, etc) • Make sure blood is DRY – if wet, must AIR DRY • Package in paper bag • Sealed bag with tape sign initial and date • For unmovable items • Dried stain - Use a sterile swab with sterile distilled water to swab the bloodstain(s) • Allow to air dry before storage • Place in sealed paper envelope/bag

  4. Types of “wet” blood evidence • Fresh, liquid blood • Use a disposable pipette and transfer to a purple top tube with EDTA • Whole blood from a living person • Whole blood from the victim and suspect is collected at autopsy or by medical professionals in a purple top tube with EDTA

  5. Blood Evidence cont. • Use purple-top EDTA tubes ONLY for DNA/Serology analysis; EDTA preserved the DNA • When refrigerated, blood in EDTA is good for approx 3-5 days • When whole blood arrives at the crime lab, make a standard bloodstain as soon as possible

  6. Examples of Dried Blood Stains • Crusts of dried blood – Scrape into a clean paper envelope or scrape into paper, then fold paper and place into paper envelope • Stained knives/rocks – submit the item without sampling – make sure knives are secured • Upholstery/rugs – Cut out section and submit to lab – Also collect an unstained portion for a control sample

  7. Dried Blood Stains - continued • Stains on walls: small stains – Photograph First - Moisten a cotton swab with water then rub stain with swab – use more than one swab if needed – If possible allow to air dry and place cotton swab in paper envelope • Submit a control cotton swab with only water • Large stains – Photograph First – Scrape blood into paper envelope or use swabs to collect blood and follow procedure for small stains

  8. Collection of Blood Evidence • Clothing – if wet with blood or other body fluid, allow to air dry naturally before it is sealed and brought to laboratory • If identification marks are made, make sure it is away from stained area • Package all clothing in paper bags – DO NOT PUT IN PLASTIC! – Medical staff will do this – Re-package when at the police department • Do not shake out clothing. If on floor in a pile – indicate order and package each item individually.

  9. Blood Evidence • How many swabs do you collect and where do you collect them? • At the discretion of the crime scene technician or individual in charge of scene • Evaluate scene and determine which stains are crucial to the case • Limited opportunity to collect stains • If there are many stains collected, understand the crime lab will not run every sample – determine which samples need to be analyzed

  10. Step 1 FIND POSSIBLE BLOOD STAINS

  11. Step 1 FIND POSSIBLE BLOOD STAINS Bloodstain Pattern Analysis • Blood stains can provide valuable evidence that can support or refute information given by witnesses or suspects. • It can also provide an investigator with a crime scene interpretation as to where and how an impact occurred, how many blows and from what sort of weapon.

  12. Step 1 FIND POSSIBLE BLOOD STAINS Bloodstain Pattern Analysis • Blood spattering is common in the scene of any injury. • The injury of artery cause blood spattering is easy to understand. • In most time, blood either falls or is thrown off often depend on some active movement.

  13. Step 1 FIND POSSIBLE BLOOD STAINS DIFFERENT SHAPES OF BLOOD SPATERINGIN DIFFERENT SPEED ,ANGLE AND VOLUME

  14. Step 1 FIND POSSIBLE BLOOD STAINS • Through the analysis the patterns of blood stains, we can determine the origin of splash and the movement of victim after he/she was wounded.

  15. Step 1 FIND POSSIBLE BLOOD STAINS Blood Spatter • Blood drops form different shapes and sizes • Blood spatter analysis uses the shapes and sizes to reconstruct the crime scene.

  16. Step 1 FIND POSSIBLE BLOOD STAINS Blood Spatter (speed) • Faster drop = larger diameter (size) • Higher distance = larger diameter

  17. Step 1 FIND POSSIBLE BLOOD STAINS Blood Spatter (volume) • size of drop also depends on the volume of the drop. • Volume depends on object blood originated from (needle = small; bat = large)

  18. Step 1 FIND POSSIBLE BLOOD STAINS Blood Spatter (Effect of Surface) • Smooth surface = smooth sphere • Rough/porous surface may cause some splatter

  19. Step 1 FIND POSSIBLE BLOOD STAINS Determining Direction of Blood • Narrow end of a blood drop will point in the direction of travel.

  20. Step 1 FIND POSSIBLE BLOOD STAINS Determining Direction of Blood If more than one drop (from spatter) results, the point of origin can be determined

  21. Step 1 FIND POSSIBLE BLOOD STAINS Determining Direction of Blood If more than one drop (from spatter) results, the point of origin can be determined

  22. Step 1 FIND POSSIBLE BLOOD STAINS Types of blood stain There are four main categories of blood stain types: • Patterns - identifiable patterns in blood such as footprints or fingerprints • Smears -identifiable patterns that show movement • Pools -area where blood has statically collected. These can show whether a body has been moved • Spattered -provide the most information about the incident

  23. Step 1 FIND POSSIBLE BLOOD STAINS Types of Spatter—Spattered Blood • 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

  24. Step 1 FIND POSSIBLE BLOOD STAINS Types of Spatter—Spattered Blood(continue) • Help determine the location of the origin of the blood source. • Help determine the mechanism which created the pattern.

  25. Step 1 FIND POSSIBLE BLOOD STAINS Types of Spatter—Spattered Blood(continue) • In general, for higher impacts, the pattern is more spread out and the individual stains are smaller. • Low impact = beating • High impact = gunshot

  26. Step 1 FIND POSSIBLE BLOOD STAINS Types of Spatter—Gunshot Spatter • Gunshot Spatter = can result in a mist-like spatter that indicates a gunshot. • Not all gunshots will result in misting. • If misting is present, it is most likely a gunshot.

  27. Step 2 PRILIMINARY TEST OF BLOOD STAINS Preliminary test —Purposes • To exclude the materials that conclusively not blood stains quickly in order to centralize our works on real blood stains .

  28. Step 2 PRILIMINARY TEST OF BLOOD STAINS Hemoglobin (have peroxidase activity ) deoxidize phenolphthalein (colorless) H2O2 [O] H2O phenolphthalein (red color) Negative result (With no color reaction) Positive result (with color reaction) Preliminary test —Principals

  29. Step 2 PRILIMINARY TEST OF BLOOD STAINS Preliminary test —Result Analysis 1 • Negative result indicating: • No blood materials in the sample ( because the test is very sensitive) • Disposition of sample when the test shows negative result: • To cast off !

  30. Step 2 PRILIMINARY TEST OF BLOOD STAINS Preliminary test —Result Analysis 2 • Positive result indicating: • There maybe some blood materials in the sample • (because the test is sensitive, everything that • has peroxidase activity should show positive result) • Disposition of sample when the test shows positive result: • To save for the following analysis

  31. Step 2 PRILIMINARY TEST OF BLOOD STAINS Preliminary test —methods • Benzidine • Leucomalachite green Phenolphthalein • Luminol and Spectrophotometric tests

  32. Benzidine blood stain

  33. Luminol reacts with the iron in haemoglobin in a chemiluminescent reaction to emit blue light

  34. Step 3 Conclusive TEST OF BLOOD STAINS Conclusive test —Purposes To make sure the materials to be studied are real blood stains

  35. 正铁血红素 血红素 变性珠蛋白 Step 3 Conclusive TEST OF BLOOD STAINS Conclusive test —Principals

  36. Step 3 Conclusive TEST OF BLOOD STAINS Conclusive test —Result Analysis 1 • Negative result indicating: • 1. No blood materials in the sample • 2. Minutes blood materials maybe in the sample ( because the test is insensitive) • Disposition of sample when the test shows positive result: • To save for the following analysis

  37. Step 4 SPECIES TEST OF BLOOD STAINS Species test —Purposes • To distinguish human from these animals

  38. Step 4 SPECIES TEST OF BLOOD STAINS Species test —Principals

  39. Step 4 SPECIES TEST OF BLOOD STAINS Species test —precipitation reaction • Precipitation • Soluble Ab + soluble Ag • Divalent Ab molecules crosslink multivalent Ag to form a lattice • Ag-Ab complex reaches a certain size and loses its solubility and precipitates out of solution • Precipitin curves are based on the amount of Ag-Ab complexes precipitated • Zone of Ab excess • Zone of equivalence • Zone of Ag excess

  40. Step 4 SPECIES TEST OF BLOOD STAINS Species test —precipitation reaction

  41. Step 4 SPECIES TEST OF BLOOD STAINS Species test —Result Analysis 1 • Negative result indicating: • Samples must not be human blood materials ( because the test is very sensitive) • Disposition of sample when the test shows negative result: • To determine which kinds of animals blood materials if necessary.

  42. Step 4 SPECIES TEST OF BLOOD STAINS Species test —Result Analysis 2 • Positive result indicating: • The sample must be human blood materials! (because the test is very specific) • Disposition of sample when the test shows positive result: • To save for the following analysis

  43. Step 4 SPECIES TEST OF BLOOD STAINS Species test —method

  44. Step 4 SPECIES TEST OF BLOOD STAINS Laboratory Analysis • If it is blood, is it Human Blood? Confirmatory tests for human blood • ABH HemaTrace cards • Species Identification tests (Ouchterlony Gel) 胶体金试验

  45. Step 5 INDIVIDUAL IDENTIFICATION OF BLOOD STAINS Individual identification — overview • The key task of forensic medicine science is to grasp the criminals! • So to find characters of criminals is most important. • Individual identification can provide biological characters of criminals! • Concluding: personal (or individual) identification is the key process of blood stains test!