Blood Poster

Aisha Rehan

Blood in Forensics

Blood is definitely one of the most important types of evidence in solving certain types of crimes. Blood has the ability to link a suspect and a victim, or a suspect to a location. It's really important because if blood evidence is documented, collected, and stored suitably, it can be presented to a judge or jury several years from the time of the criminal act and can absolutely eliminate a person as a potential suspect in a crime.

Famous 16-year old Texas girl Muder

Ricky McGinn was tried for the horrific rape and murder of a 16 year old Texan girl in 1994. He had been previously accused of murder, rape and molestation. Bloody evidence including a hammer found in his car, and drops of blood on his shoes matched the victim’s type.


Also, in 2000, after years on death row, an appeal was made to Governor George W Bush to test DNA on a single pubic hair found in the victim’s private parts. Governor Bush granted a stay of execution based on a brief filed by Barry Scheck, OJ Simpson’s lawyer, and tests were made and verified. The DNA matched McGinn, and his execution was carried out September 27, 2000.

Forensic Terminology

Serology--what is it?

Forensic serology is the detection, classification and study of various bodily fluids such as blood, semen, fecal matter and perspiration, and their relationship to a crime scene. A forensic serologist may also be involved in DNA analysis and bloodstain pattern analysis.

Plasma

Blood is the liquid part of the human body, which is called Plasma. Plasma contains proteins, clotting factors, electrolytes, and a varying number of cells.

Antibodies

Antibodies are proteins secreted by white blood cells that attach to antigens.

Antigens

Antigens are any foreign substance or cell in the body that reacts with antibodies.

Erythrocytes

Erythrocytes are red blood cells. They are produced in the bone marrow and contain a protein called hemoglobin that carries oxygen to our cells.

ABO

Forensics useS a system called the ABO System, which involves examining the surface of the red blood cells for two antigens known as A and B, with blood type being named after the type of antigens it contains, including A, B, AB and O. The basic foundation of serology states that for every antigen, a specific antibody is in existence.

Rh

Rh factor is any of a type of specific antigen present on the surface of red blood cells; persons having inherited such antigens being designated Rh+ (Rh positive) and persons lacking them, a much smaller group, being designated Rh− (Rh negative) blood of Rh− persons is incompatible with Rh+ blood because of antibody reaction.

Leukocytes

Leukocytes are white blood cells and a type of blood cell that lacks hemoglobin and is therefore colorless.

Platelets

Platelets job is to protect the body from exposed cuts. They basically clot together through a process called coagulation to seal a wound and prevent loss of blood.

Hemoglobin

Hemoglobin is a red protein responsible for transporting oxygen in the blood of vertebrates. The Kastle–Meyer test is a presumptive blood test in which the chemical indicator phenolphthalein is used to detect the possible presence of hemoglobin, which can be used to chemically identify blood.

Blood Factors

Theoretically, no one, except identical twins, has the same combination of blood factors. In the forensic-science world, blood-factor identification is not yet practical as a means of individualization.

Serum

Serum is yellowish and contains white cells and platelets. With serum, a forensic analyst can determine the freshness of a blood sample because serum clots several minutes after exposure to air. Antibodies are also found in serum which have important forensic implications.

Fun Facts

  • Luminol is a powder made up of oxygen, nitrogen, hydrogen, and carbon that glows blue when it comes into contact with the hemoglobins in blood.
  • Luminol can detect minute amounts of blood even after an area has been washed-- even years later.
  • A human must lose approximately 40% of his or her total blood volume before they are at risk for death from blood loss.
  • Blood spatter analysis can be essential in determining the type of weapon used during a crime.