You were lying on your shag carpet watching television while petting your Yorkshire Terrier. You walk through some dirt on your walkway before entering your car and placing your feet on the carpet of your floor mat.
Now, you go to a grocery store but hop across a flower bed with fresh potting soil in it - a specific mix of Nitrogen, Potassium and Phosphorous - someone was working on it earlier today!
After going to the store, you come back home. Now....each place you went and everything you touched transferred from one location to another. In your home, you'd find traces of the potting soil from the grocery store parking lot and in the grocery store, you could find (if you knew how to look for it) your dog hairs, carpet hairs at home and from your car and the dirt from your walkway.
Also, on your body and clothing are tiny pieces of evidence of where you've been all day! Annoying right? Not for crime scene investigators! This is the type of evidence that most criminals do not have the training or knowledge on how to prevent!
Here are some types of trace evidence that you can pick up and transfer throughout the day. These can all ultimately be considered as pieces of evidence at a crime scene:
- Hair from your body, your pets, your friends and family.
- Fibers from the carpets you've walked on or sofas you have sat on or even brushed against
- Dirt from floors, walkways, flower beds, gravel drives, etc.
- Fibers from ventilation systems
- Paint chips from walls, cars, furniture
- Plant material from the floor or a lawn / park / walkway
- Fibers from your clothing such as a mohair sweater
FBI Training Video: Examination of Hair and Fibers, Tires and Shoe Impressions
http://thefilmarchive.org/ Fiber analysis is a method of identifying and examining fibers used by law enforcement agencies around the world to procure evidence during an investigation. Fiber analysis is also used by law enforcement agencies to place suspects at the scene of the crime. Transfer of fiber can occur during close contact with the victim or suspect. Fiber transfers can also occur during break-ins where fibers from the intruder are caught in broken glass or window screens. This method is usually not used to actually pinpoint an offender in an investigation as t is not as reliable as DNA. Fiber analysis does not follow any officially laid-down procedure. The most common use of fiber analysis is microscopic examination of both longitudinal and cross sectional samples. While this is the most common method of undertaking fiber analysis, others do exist. These include the burning and solubility methods. These methods are most commonly used to reveal the identity of the fiber. Fiber analysis is usually not undertaken in university labs because of the usual lack of required solvents. Scanning Electron Microscopy (SEM) is method of photography which requires an instrument called the scanning electron microscope, which uses electrons rather than light to form an image. There are many advantages to using the SEM instead of a light microscope. Using SEM requires a large depth of field which allows a large amount of the sample to be in focus at one time. Atomic force microscopy is a method which is carried out using a Atomic Force Microscope which is an instrument that can analyze and characterize samples at the microscope level. The instrument allows the analyst to look at surface characteristics with very accurate resolution ranging from 100 μm to less than 1μm. http://en.wikipedia.org/wiki/Fiber_analysis
Trace Evidence Pt. 1
Trace Evidence Pt. 2