CSI And Trace Evidence
What is 'trace evidence' and how is it studied in CSI?
Trace evidence is just what it sounds like. It's minute items of evidence. Sometimes evidence that can't even be seen with the human eye and must necessitate the collection of items that are carriers of trace evidence. But trace evidence is just what the word says. It's minute items that must be brought back to the lab for examination, certainly microscopic examination and other sensitive technologies must be brought into play to deal with those items of evidence.
What is the 'exchange principle' of CSI?
The exchange principle came about as a result of the work of Edmond Locard who in 1915 founded the first crime lab in the world in Leone, France. He was very much interested in dealing with dust particles and items of trace evidence. He espoused the concept that every contact leaves a trace, and that gave rise to what we call The Locard Exchange Principle. That is the basic principle of underlined trace evidence analysis and trace evidence investigations today - every contact leaves a trace.
How does studying hair help in CSI?
Hair in that deposition, that crime scene, comes about often as a result of violent contact between the suspect and the victim and because of that, it's usually a crime of very serious nature. It could be sexual assault, it could be a murder. So, the finding of a hair at a crime scene and the ability to link that hair to a particular individual certainly incriminates that individual and raises significant suspicions. But, there's more work that has to be done in order to complete the analysis of human hair examination, and that entails, also, DNA.
What parts of a hair are studied in CSI?
We look at the root, we look at the tip, and we look at the body of the hair. We look for all the morphological characteristics that one can find with a microscope. What's very important also the color of the hair, the thickness of the hair, and the microscopic characteristics that we see under the scope. We would then compare those to characteristics to other hairs to see if we can make a link.
What can be learned from studying hair samples in CSI?
There are a number of things that can be learned from studying hair samples in CSI. Of course most importantly we can learn whether a particular individual can be included or excluded from a crime scene. Now certainly if the hairs do not compare, that will serve to exonerate an innocent individual. But if we have a hair comparison, where there is a comparison or a likeness that warrants further study, utilizing hair to determine the sex of an individual, to determine the race of an individual, to determine the age of an individual is a very risky proposition that should be undertaken with a very good deal of caution, and it is really not recommended that that kind of analysis be conducted just from human hair. Probably the best thing we can do with a human hair would be to link it or not link it with a particular individual by a microscopic examination.
What types of fibers are studied in CSI?
There are basically two types of fibres that are studied in CSI. There are natural fibres such as cotton and wool, and there are man made fibres such as nylon, polyesters and acrylics. And those are the two major categories of fibres that forensic analysts are trained to work with.
What do forensic scientists measure when comparing fibers?
It depends on the nature of the fiber. If it is a natural fiber such as cotton or wool, the microscope is the key tool. They are looking at the thickness, the color of the fiber, and the morphologic characteristics as observed underneath the microscope is key to that examination. If, however we're dealing with man-made fibers, there are microscopic considerations to be made such as the color, the thickness, and the morphological characteristics. But also we will look at the chemical aspects of that fiber. We will look at its chemical composition. We will look to see and we can characterize the color of the fiber, through the spectral analysis. It is a much more complicated and lengthy procedure to do a man-made fiber analysis as opposed to natural fiber.
