Forensic science is the application of scientific techniques in collecting and analyzing physical evidence in criminal cases. 1 Forensic science has really advanced over the years. The first recorded application of medical knowledge to the solution of a crime was in a Chinese book, His Duan Yu (the washing away of wrongs), written in 1248. It contains a description of how to distinguish drowning and strangulation. These days, we have ways of telling whether the person was drowned intentionally or not and if their strangulation was accidental or a murder.
There are many branches to the world of forensic science. There are: firearms and tool mark identification, forensic psychiatry and profiling, criminal law, personal identification, forensic photography, and crime scene processing. These all require deferent scientists to do, because of how long it takes to do the work. A crime may have as many as ten forensic experts looking for evidence and examining it.
First let's look at firearm identification. Physical evidence has two main parts: class characteristics and individual characteristics.
"Class characteristics are characteristics that are common to a group of similar objects. For example, someone buys a pair of Nike Shock sneakers. All Nike Shock sneakers have to same shape and same tread design on the bottom. These are class characteristics. Individual characteristics are those characteristics that are unique to a given object and set it apart from similar objects. You wear your sneakers around for a while and they get worn. The treads wear down. They get little pits and gouges in them. These little pits and gouges are individual to your shoes and no others since no one has walked over the exact same surfaces in the exact same way in their sneakers. These two concepts, class and individual characteristics are the most important in firearms examination. 2
A firearms examination is basically matching a bullet