There are many different types of evidence found at a crime scene. Any of these could be a significant piece in solving the crime. The significance of each piece of evidence is often unknown until after the evidence has been bagged, labeled, and sent to the lab. For these reasons, forensic scientists treat each and every piece of evidence as if it is vital. Every object at a crime scene is considered to be significant until toughly examined. More often than not, the forensic scientists only obtain usable evidence from a small percentage of the objects collected at a crime scene. It may seem that much examination of evidence is fruitless, but the discovery of unexpected evidence such as a finger print or hair, can break and investigation wide open.
There are several different kinds of analysis which can be performed on each type of physical evidence. Almost all evidence requires one or more types of analysis to yield the most complete information. Most analysis fits into one of the following categories:
Types of Analysis
Comparison Most types of evidence require a control with which to be compared (example: fingerprints, hairs)
Visual If evidence can be utilized or compared through unaided observation, then that analysis is called visual (example: fingerprints, tool marks)
Microscopic A microscopic analysis indicates that evidence must be observed with the use of some type of microscope (example: hairs, fibers)
Chemical If an article of evidence must be subjected to any type of chemical procedure to be best utilized, that article requires chemical analysis (example: DNA typing, drug screening)
Common Types of Physical Evidence
Documents. Any document, hand- or typewritten, will be submitted so that authenticity and source can be determined. These types of analysis are utilized mainly with ransom notes, suicide notes, death threats, and forgeries. When typewriters were used, it was quite simple to match a machine to its productions. With the development of inkjets and laser printers, matching printed documents have become nearly impossible. The exception would be if a document were to be printed with an uncommon font or with a rare ink.
Since the diminished use of typewriters, document analysis is now primarily concentrated on handwritten documents. Although each person’s handwriting is original, no one reproduces writings in the same way twice. Forgers are resourceful and inventive during their attempts to reproduce signatures. For these reasons, handwriting analyses rarely provide a 100% match.
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Glass. Glass panes, particles, or fragments that are found or transferred to a person or object involved in a crime may be substantial evidence. Such evidence, whether broken by a bullet or other means, may link a suspect or piece of evidence to a crime scene, and be used to deduce cause of breakage or direction of penetration. Additionally, it is common for fingerprints and/or blood to be present on broken glass.
Soils, Minerals, Wood, and Other Vegetative Matter. Any items containing soil, minerals, wood, or other vegetative matter could link a person or object to a particular location (for example, soil imbedded in shoes and vault insulation found on garments).
Most samples of such are unable to prove make match, but may with the presence of a rare material. Often such types of evidence are considered circumstantial, but are useful in supporting other evidence in a case.
Fingerprints have long been a mainstay in criminal investigating. It is widely known that when a person touches an article with their bare hands that a print is left behind. Such prints are called latent prints. The challenge for the forensic chemist is to develop, or make visible, these