A crime lab technician looking for prints  (AP)

Forensic science is the application of scientific knowledge and method to law.  The agencies that enforce the laws depend on technicians who can collect and analyze key pieces of information at crime scenes.  That involves biology, chemistry, physics, anthropology, geology, and computer science.  What goes on in a crime scene laboratory is known as criminalistics, which is the collection and analysis of physical evidence.  Not all forensic scientists are criminalists, but all criminalists are forensic scientists.  

The oldest forensic science laboratory in the United States was created in 1923 in Los Angeles, California.  Police chief August Vollmer headed the first university-affiliated institute for criminalistics and criminology (the study of criminal character).

When the FBI organized a national laboratory for forensic science in 1932, it was the first centralized way to offer a variety of forensic services to law enforcement agencies around the country.  It is now the world's largest forensic lab, and its structure serves as a model for state and local laboratories.  In 1981, the FBI opened the Forensic Science and Research Training Center, which was dedicated to developing new technologies and to training crime lab personnel.

Skeletal bones laid out for examination (AP)

Crime labs operate at federal, state, county and municipal levels.  There is no single model that represents them all, in part because of budget restrictions for purchasing equipment and hiring personnel.  Most are affiliated with police departments, some are under the direction of the district attorney or the coroner, and universities oversee a few.  In any given lab, there may be one lone technician or over one hundred.  They may generalize, with each person doing a range of jobs from photography to DNA, or they may specialize in such things as soil analysis or DNA.

A full service crime lab for a large city would include an evidence collection unit that is trained in what to look for and how to collect and preserve evidence to avoid corruption.  Taking this evidence back to the lab means submitting it to one of the following:

1. Physical science unit – this involves the use of chemistry, geology, and physics for analyzing evidence.  Most trace evidence, such as glass fragments, soil, explosives, non-natural fibers, and paint are analyzed here. 
2. Biology unit – biological specimens such as tissue, semen, hair, and blood are scrutinized in this area, including any DNA analysis.  This unit will also look at plant samples and other botanical materials, as well as some fibers.
3. Firearms/Ballistics Unit – The technicians examine guns, expended bullets, cartridge cases, and gun powder residue to provide information about effects of shooting from different distances, and matching a fired bullet to a particular gun.  They may also analyze tool mark impressions.
4. Document Examiners – Documents of unknown origin include forgery analysis, bad checks, anonymous handwritten or typewritten samples, and ransom notes.  Examiners analyze authorship and authenticity, including the materials used to produce the document.
5. Photography – All crime scenes must be photographed, including autopsies done on a homicide victim.  These experts also help to assemble photographs for courtroom exhibits.  The lab has different types of cameras and film, along with an inhouse darkroom.
6. Identification Unit – examining and collecting fingerprints for comparison to a database or to a suspect is the province of this unit.  They may also do footprints and tire impressions.
7. Evidence storage section – evidence must be stored in a secure place with a clear protocol for receiving the evidence and for keeping track of the chain of custody so that it does not get lost

Other services performed by a crime lab may include:

1. Toxicology (drugs and poisons in tissues or body fluids)
2. Polygraph ( a device to aid in the detection of deception)
3. Voiceprint ( a device used to identify an individual's voice)
4. Arson
5. Impression evidence

The instruments for evidence analysis that a well-stocked lab may have include:

• Different types of microscopes
• gas chromatograph
• x-ray diffraction unit
• emission spectrograph
• mass spectrometer
• atomic absorption spectrophotometers
• electrophoresis equipment
• sound spectrograph
• computers for databases
•  refractometers

While it's beyond the scope of this article to cover how each type of evidence is processed, let's look at the development of one method that has long been a mainstay of crime scene investigation: fingerprinting.