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Last updated on October 13, 2007
Introduction
This particular subject is not entirely based on crime scene investigation. We will first look at blood types as that is one method of linking a person to a crime scene. More importantly, it can be a first method of excluding someone from suspicion. Do you know your blood type? Read on........
Assignment One
The distribution of blood types A - B - O - AB among Americans are as such:
A = 40% of the population
B = 11% of the population
O = 45% of the population
AB = 4% of the population
So if a crime is commited in New York City, a city with a population of 8 million, and the blood type of the perpetrator is identified as AB how many people can be ruled out based on blood type alone? You can view the maps on Blood Type Distribution and see that blood type percentages are not the same in every part of the world. In South America, for example, the population has predominantly what type of blood?
Assignment Two
As we learned in Unit Four DNA can be extracted from blood to identify and convict a criminal. Aside from blood types and DNA evidence what other details can blood provide about the crime? In some particularly violent crimes blood spatter or footprints could provide valuable information. Let's look at some Terminology associated with blood spatter evidence. Choose five separate terms and rate them on a scale of 1 to 10 as far as how important you think they are to a crime scene. Remember that every scene is different and that what may be crucial at one crime may not be so valuable at another. Read the passage on Blood Spatter Interpretation and answer the following questions:
Give three factors that can be determined from blood evidence.
What factors can help to trace a blood sample back to it's point of origin?
In which direction will a drop of blood be pointing?
What does it mean to say that bloodstain evidence is predictable and reproducible?
Scan this Bloodspatter article and describe what mathmatical concept can be used to determine the point of origin of a blood drop.
Assignment Three
Take a clean sheet of paper, a pencil, two cups of different colored water and try this:
Draw a dotted line down the center of the paper. Dip the pen in one color of water and shake it towards the center of the paper with your right hand. Observe the pattern of the spray. Now do the same with the pencil in your left hand and with the second color of water. Can you see the direction that the drops are pointing? Write down how the patterns are different from one another.
Assignment Four
Another significant factor of blood is it's ability to clot. Blood needs to clot in order to stop bleeding when someone is cut. If you do not have blood that clots well you stand to lose a good portion of your blood relatively quickly. Clotting is also important at a crime scene as it can tell how much time has elapsed since a wound was inflicted. Read this article on Clotting and answer the following questions:
List three factors that can affect the clotting of blood.
If blood is found in a shiny, gelatinous pool, how long ago did the bleeding occur?
What is the difference between a passive and projected bloodstain pattern?