Forensic Geology89.215

Professor Lori Weeden

Forensic Geology: That branch of the earth sciences that uses rocks, minerals, fossils, soils, and a variety of geochemical techniques to provide physical evidence in criminal investigations and trials.

Forensic Evidence can be of two types:

1) Individual – items that can have only one source. Examples are fingerprints, some tool marks, bullets, DNA. etc.

2) Class – items that can come from a variety of sources. The value of a class item depends on its uniqueness. For example, paint scrapings from a car may identify the year, make, and model of the car, but not the specific vehicle. The usefulness of the evidence would depend on how common this car was in a particular area. Most geological evidence is of the class type.

Physical evidence is generally more reliable than human evidence (eyewitness accounts).

Let’s test this hypothesis….

The suspects…

The weapons…

Let’s go for a walk….

Dr. Eby…

The box exercise

You have 2 minutes to look over the contents of the boxes…

Put the boxes away and write down what you remember.

Take the boxes out again and try to determine a sequence of events. (While you’re there, check your memory from the previous exercise, was it close?)

What have these exercises taught you about the reliability of eyewitness testimony?

Keep in mind that you, as a group, are more prepared and observant than the average person, simply because you are taking this class.

Is it possible to make your physical evidence support your belief that a suspect is guilty? Would this be a proper use of physical evidence?

In the United State of America a suspect is considered innocent until proven guilty. You MUST remain objective with physical evidence. Physical evidence or more specifically class-type evidence is only as good as the examiner and subsequent statistical findings.

“ Wherever he steps, whatever he touches, whatever he leaves, even unconsciously, will serve as a silent witness against him. Not only his fingerprints or his footprints, but his hair, the fibers from his clothes, the glass he breaks, the tool mark he leaves, the paint he scratches, the blood or semen he deposits or collects. All of these and more, bear mute witness against him. This is evidence that does not forget. It is not confused by the excitement of the moment. It is not absent because human witnesses are. It is factual evidence. Physical evidence cannot be wrong, it cannot perjure itself, it cannot be wholly absent. Only human failure to find it, study and understand it, can diminish its value.”

- Professor Edmond Locard

Locard’s exchange principle

Locard’s exchange principle

Locard's principle is applied to crime scenes in which the perpetrator(s) of a crime comes into contact with the scene, so he will both bring something into the scene and leave with something from the scene. Every contact leaves a trace.

For this class we will consider soil, clay, sand, minerals, fibers and fossils as evidence. We will examine these items in a variety of manners best fitting the details needed for the investigation.

For class next week, go to the web page, under “Dr. Eby’s web page”, print out “Sand size-distributions as evidence…” and be prepared answer questions about and to conduct this exercise.

http://environmental.geochemistry.googlepages.com/forensicgeology