Measuring the quantity of alcohol in the blood is one of the three methods available to assess alcohol impairment. This is usually accomplished by an instrumental chemical analysis of the blood to measure the blood-alcohol concentration. A practical method for monitoring alcohol impairment in driving is breath analysis via breath testing devices. These breath analyzers measure the amount of alcohol in breath and translate it to blood-alcohol levels.

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Arson investigation is the science of determining the cause of a fire. It is necessary for experts in this field to be knowledgeable in scientific, as well as non-scientific areas. Such scientific areas include physics, chemistry, and electronics. An extensive knowledge of the construction of buildings would be an example of a non-scientific area. It is also important for an arson investigator to be aware of the psychological disorders that are related to fire-setting behavior.

Investigation of explosives is similar to investigation of arson, since the explosion scene requires extensive reconstruction efforts. The investigator must be knowledgeable in the areas of manufacture, materials, and detonation of explosive materials. Another important aspect is the knowledge of the mental states and psychological disorders that lead to random and intentional bombings.

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Crime scene investigation entails the preservation and collection of evidence located at the scene of a crime. Crime scene reconstruction is the interpretation of the evidence to recreate the circumstances of the crime. Each crime scene is unique and must be evaluated individually.

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Forensic biology is the study of body fluids: blood, saliva, semen, and urine.

From biological evidence left at a crime scene, such as hair or semen, DNA analysis (or DNA typing) can help to identify an individual. The most widely used methods of DNA typing are short tandem repeat (STR) typing and mitochondrial DNA (mtDNA) typing. Both methods use the polymerase chain reaction (PCR) to amplify the DNA extracted from a biological sample, thereby increasing the sensitivity of the analysis. STR typing yields information about chromosomal DNA, whereas mtDNA typing yields information about DNA in mitochondria.

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Toxicology is the study of substances that are harmful to humans. Toxicologists examine body fluids and organs for the presence of poisons, alcohol, and drugs. A toxicologist detects, identifies, and quantifies minute amounts of these substances for further evaluation.

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The basic principle of firearms examination is that most machined parts will have unique marks, which can be transferred to other surfaces. Almost all gun barrels, as well as the machined areas in the weapon’s firing mechanism, leave unique marks on bullets fired through the barrel and on cartridge cases propelled through the firearm. A firearms examiner examines both firearms and ammunition of all types. The firearms examiner also determines whether a bullet originated from a suspect firearm. Impacted items on the receiving end of a discharged bullet are also examined for discharge residues in an attempt to ascertain muzzle distance.

As each machined gun barrel is unique, so too are all machined tools. Tools leave distinct marks on most objects they contact. A toolmark is any machined impression transfer caused by the tool coming into contact with an object. A toolmark examiner compares toolmarks in order to determine what type of tool, or what exact tool, was used to make a specific mark.

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A latent print expert examines all types of fingerprints found at a crime scene, whether visible or not. The three categories of fingerprints include: latent, plastic, and contaminated. Latent fingerprints are the invisible prints made by the deposit of oils or perspiration from the friction ridges of one’s fingers onto a substance. Plastic prints are those fingerprints impressed into easily malleable surfaces, such as plasticine clay or putty. Contaminated fingerprints are the result of material transfers, such as liquid blood, from the fingers to a surface.

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A questioned documents examiner analyzes and identifies written, printed, or typed material for authenticity. If the authenticity is doubted or if its source is unknown, it becomes a questioned document. Questioned document examination may be associated with criminal cases involving forgery, suicide, and embezzlement.

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Examples of trace evidence are hair, fibers, paint chips, or glass fragments. Trace evidence is often of such a minute nature that it can be easily cross-transferred from one surface to another without detection; therefore, the microscope is usually the first tool used in its examination and identification. Instrumental methods of analysis are generally the second phase of comparison associated with trace evidence.

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