Forensic Science:Blood Analysis and Blood Spatter at a Crime Scene

By: Monica Ye & Lilliana Mendoza Mentor: Dr. John Molina Bronx Community College

Blood is a mixture of cells, enzymes, proteins, and inorganic substances.

The fluid portion of blood is called plasma, which is mostly contains nutrients and dissolved proteins.

The other portion of blood is the cellular phase. This contains red blood cells, white blood cells, and platelets.

Antigens are proteins located on the surface of red blood cells and are responsible for blood type characteristics.

The most important types of antigens are A-B-O. Type A has A antigens in one’s red blood cells. Type B has B

antigens. Type AB has AB antigens, and type O has neither A nor B antigens.

Nature of Blood

For every antigen there is a specific antibody that will react with the antigen to form clumps known as agglutination. For example, if anti-B is added to red blood cells carrying B antigen; there will be a reaction.

The blood that is found a crime scene contain Deoxyribonucleic Acid (DNA).

DNA is found in the nucleus of cells which contains the genetic material of living organisms.

DNA is used to identify the victim(s) and the killer involved.

Blood can also be used to determine the sequence of how a crime occurred.

The blood that is found can be used to determine what weapon (if any) was used in the crime.

Blood can also help identify the origin of the blood.

Importance of blood at a crime scene:

When blood is found at a crime scene, it is possible that the substance may not be blood at all.

A preliminary or screening test procedure is used to determine if the substance is blood; this preliminary or screening test procedure is called Presumptive Testing.

Presumptive Testing is based on the reactivity of hemoglobin, a protein found in red blood cells used to carry oxygen throughout body. Two different chemicals are used in this test: Phenolphthalein and O-toluidine.

Identifying Blood

How are the chemicals used? - A sample of the blood is taken on a Q-tip and a small

amount of the chemical is dropped on to the sample. - If the substance is blood, when Phenolphthalein is used;

the sample will turn pink. If O-toluidine is used; a green-blue color will appear. When these colors appear, it doesn’t necessarily mean that it is blood. The blood sample needs to undergo another procedure that confirm the presence of blood.

Both Phenolphthalein and O-toluidine reacts to the Hemoglobin, which is an oxygen- carrying protein in the red blood cells.

A sample of the blood is placed on a slide and examined under a microscope.

If the substance is blood crystal-like shapes will form.

If the substance is not blood no crystals will form.

The Takayama Test

After we confirm that the substance found is blood at the crime scene; PCR analysis is used. PCR stands for ‘polymerase chain reaction’. This is a technique that is used to create millions of copies of DNA just using a single sample of DNA.

This technique is used by forensic scientists to perform DNA analysis on really small samples; such as skin cells.

So from the blood substance, DNA is extracted and then analyzed using this procedure.

Other tests may include: STR (Short Tandem Repeat testing), RFLP (Restriction Fragment Length Polymorphism).

PCR Analysis

Blood spatter is a group of blood stains resulting from one or more injuries.

Spatters are produced in different ways; such as stabbing, gunshots, beatings, cast-off blood, and splashing.

Careful study of these spatters can help forensic scientists to figure: -out the origin of the blood stains -type of weapons used -the direction which the object struck the victim -movements of the victim and the suspect -the number of blows and gunshots the victim received -sequence of events

Blood Spatter

There are three basic types of blood stains: - Passive: are blood drops created or formed by the

force of gravity alone. - Transfer: is created when a wet, bloody surface comes

into contact with another surface. - Projected: are created by more force or action greater

than gravity.

Categories of Blood Stains

-When a blood drop is dropped from a 90 degree angle, the drop is round and the length as well as the width would be equal.

-When blood falls at an angle less than 90 degrees, its shape would resemble a teardrop.

-The pointed end of the blood stain is called the “tail” and it would always point in the direction of the travel of the blood.

Direction of Blood Stain

-At a 90 degree angle, the blood drop is circular and there won’t be any short or long axes.

-Below 75 degrees, the spines become more prominent on the side of the spatter opposite the angle of impact.

-At highly acute angles; usually below 40 degrees, the blood drop begins to form tails and a second spatter coming from the first one.

-The angle of impact can be determined by taking the inverse sine of the width over the length of the blood stain.

Angle of Impact

Example: SIN = Width (a) 1.5cm Length (c) 3.0cm Width (a) 1.5cm = 0.5 = SIN Length (c) 3.0cm

= 30O

Slemko, J. "BLOODSTAIN PATTERN ANALYSIS TUTORIAL." Homepage. Web. 28 July 2009. <http://www.bloodspatter.com/BPATutorial.htm>. Forensic Science Service Ltd. "Forensic Science Service - Blood Pattern Analysis." Forensic Science

Service - Home Page. Web. 28 July 2009. <http://www.forensic.gov.uk/html/services/analytical-solutions/blood/>.

Mindrelief.net. "Blood in the Crime Scene." Custom essay, term paper, research paper writing service. Web. 30 July 2009. <http://www.mindrelief.net/blood.html>.

Old Spring Harbor Laboratory. "Cutting, Pasting, & Copying DNA & the Recombinant DNA Controversy." DNA Interactive: Discovering the DNA Structure and beyond. Web. 03 Aug. 2009.

"RFLP Definition." Www.FoodSafety.gov - Gateway to Government Food Safety Information. Web. 05 Aug. 2009. <http://www.foodsafety.gov/~frf/rflp.html>.

"RFLP Definition." Www.FoodSafety.gov - Gateway to Government Food Safety Information. Web. 05 Aug. 2009. <http://www.foodsafety.gov/~frf/rflp.html>.

PBS. "A Science Odyssey: DNA Workshop: Replication." PBS. Web. 03 Aug. 2009. <http://www.pbs.org/wgbh/aso/tryit/dna/replication.html>.

"RFLP Definition." Www.FoodSafety.gov - Gateway to Government Food Safety Information. Web. 05 Aug. 2009. <http://www.foodsafety.gov/~frf/rflp.html>.

Think Quest. "Forensic Science | Blood Analysis." Oracle ThinkQuest Library. Web. 05 Aug. 2009. <http://library.thinkquest.org/04oct/00206/lo_pti_blood_analysis.htm>.

http://www.bloodspatter.com/terminology.pdf http://www.nfstc.org/links/animations/images/blood%20spatters.swf

References

o Dr. John Molinao Dr. Sat Bhattacharyao Bronx Community Collegeo National Science Foundation o Harlem Children Societyo Harlem Children Society Staffo Audience

Acknowledgements

Thank You!