How is Blood Evidence used in Forensics?

1
How is Blood Evidence used in Forensics?

• Provide information about how blood evidence is
  collected, categorized and compared.
• How do scientists determine if a fluid is blood?
• Are those tests foolproof?

2
How blood evidence is collected

• Blood pool collect with gauze pad or clear
  cotton. Let air dry and refrigerate of freeze
  within 48 hours.
• Dried blood wrap object in clean paper and place
  in paper bag.
• Small object, send whole object in.
• Large object, cover with paper and tape down or
  scrape it off with a knife.

3
How blood evidence is categorized and compared

• Bloodtypes- A, B, AB, or O
• Antiserum A or Antiserum B to determine type
• Rh factor is most commonly know antigen but there
  are over 256.
• Dried blood-
• Heat sample to break antibody antigen bonds
• Add know blood group to see what coagulates.

4
How scientist determine if a fluid is blood

• Use Luminol to determine if blood is present, but
  once luminol is used it destroys the blood for
  further testing.
• Takes 5 second to read.
• Luminol cause blood to glow.
• Dried blood
• Takayama and Teichmann -crystallization test
• Kastle-meyer chemical phenophthalein turns it
  pink if there is evidence of blood.
• Precipitin determines if it is animal or human
  blood

5
Foolproof?

• No
• Other substances may react with chemical used
• Blood degrades
• Evidence of Chimerism
• Secretors

6
Websites used

• Collection and Preservation of Blood Evidence
  from Crime Scenes, by George Schiro, Forensic
  scientist Louisiana State police Crime
  Laboratory http//www.crime-scene-investigator.ne
  t/blood.html
• http//www.crimelibrary.com/criminal_mind/forensic
  s/serology/four.html
• http//nobelprize.org/educational_games/medicine/l
  andsteiner/readmore.html
• http//www.faculty.ncwc.edu/TOCONNOR/425/425lect13
  .htm