Criminalistics is the forensic science of analyzing and interpreting evidence using the natural sciences. Forensic science pertains to all sciences applied to legal problems. CRIMINALISTS use the science of criminalistics to solve crimes. They examine and identify physical evidence to reconstruct a crime scene. Physical evidence can be a weapon, a piece of clothing, a bloodstain, drugs, or even a vapor in the air. Criminalists use this physical evidence to provide a link between a suspect and the victim. The transfer of clothing fibers or hair fibers between a suspect and the victim can provide just such a link. Fingerprints, bullets, and shoe impressions are other important links.

Physical evidence is collected from a crime scene that includes the victim's body and the surrounding area of the crime. Criminalists collect physical evidence at crime scenes and receive evidence at the laboratory, which has been collected at the crime scene by crime scene investigators. The proper collection of evidence is essential to prevent contamination and destruction of the evidence. Once the evidence is brought to the crime lab, Criminalists conduct tests depending on the type of evidence. Criminalists are often called to court to provide expert testimony regarding their methods and findings.

O*NET typical tasks include the following:

• Examines, tests, and analyzes tissue samples, chemical substances, physical materials, and ballistics evidence, using recording, measuring, and testing equipment.
• Interprets laboratory findings and test results to identify and classify substances, materials, and other evidence collected at crime scene.
• Collects and preserves criminal evidence used to solve cases.
• Confers with ballistics, fingerprinting, handwriting, documents, electronics, medical, chemical, or metallurgical experts concerning evidence and its interpretation.
• Reconstructs crime scene to determine relationships among pieces of evidence.
• Prepares reports or presentations of findings, investigative methods, or laboratory techniques.
• Testifies as expert witness on evidence or laboratory techniques in trials or hearings.

Serology is the analysis of body fluid evidence that includes bloodstains, semen stains, and saliva. To determine the identity and origin of the substance, Criminalists analyze blood dried into fabrics or other objects, as well as cigarette butts that may contain saliva residues. Sometimes the stain is not visible to the naked eye. Blood is usually visible due to its color, but often an artificial forensic light source is necessary to see other body fluid evidence. The stained evidence must remain dry and be stored at a cold temperature to maintain its integrity.

DNA typing is possible with a sample of body fluid such as blood, saliva, or semen. DNA typing provides a Criminalist with a genetic blueprint that is unique to each person. Criminalists then try to match the DNA typing results with a suspect. Proper handling and storage is essential to preserve DNA test samples.

Trace evidence is the analysis of hairs, fibers, paint, glass, wood, and soil that are present at a crime scene. Examination of trace evidence helps to establish a relationship between a suspect and the victim. A fiber may be taken from the victim's body revealing the type of fiber from carpet unique to the make and model of the suspect's car. Once trace evidence is discovered, a Criminalist or other investigator collects the evidence from the crime scene by using a pair of jeweler's tweezers and immediately places the evidence in a folded paper cone and then into a sealed evidence envelope. Trace evidence is later analyzed at the crime lab to determine its composition and origin.

Firearms and toolmarks analysis involves the examination of any firearm that is suspected of being used in a criminal act. Criminalists can determine the kind of bullet used and whether it was fired from the gun used to commit the crime. Toolmark analysis includes any object suspected of containing the impression of another object that served as a tool in the commission of a crime. For instance, a screwdriver makes a distinctive impression when scraped along the surface of a wall. A Criminalist will analyze the marks the screwdriver left behind.

Impression evidence is the evaluation of impressions made by shoes, tires, depressions in soft soils, and all other forms of tracks and impressions. Glove and other fabric impressions, as well as bite marks in skin or food, are included. Criminalists also obtain impressions of dust from surfaces to reveal fingerprints.

Drug identification is used by Criminalists to analyze and identify illegal substances such as cocaine, heroin, and marijuana, that are found in plastic bags or vials at crime scenes. Criminalists must interpret the results of drug analyses in order to determine their significance to the case.

Important skills, knowledge, and abilities Criminalists need to do their jobs are:

• Information Gathering - Knowing how to find information and identifying essential information.
• Information Organization - Finding ways to structure or classify multiple pieces of information.
• Reading Comprehension - Understanding written sentences and paragraphs in work related documents.
• Problem Identification - Identifying the nature of problems.
• Science - Using scientific methods to solve problems.
• Critical Thinking - Using logic and analysis to identify the strengths and weaknesses of different approaches.
• Chemistry - Knowledge of the composition, structure, and properties of substances and of the chemical processes and transformations that they undergo. This includes uses of chemicals and their interactions, danger signs, production techniques, and disposal methods.
• Public Safety and Security - Knowledge of weaponry, public safety, and security operations, rules, regulations, precautions, prevention, and the protection of people, data, and property.
• English Language - Knowledge of the structure and content of the English language including the meaning and spelling of words, rules of composition, and grammar.
• Inductive Reasoning - The ability to combine separate pieces of information, or specific answers to problems, to form general rules or conclusions. It includes coming up with a logical explanation for why a series of seemingly unrelated events occur together.
• Oral Expression - The ability to communicate information and ideas in speaking so others will understand.
• Information Ordering - The ability to correctly follow a given rule or set of rules in order to arrange things or actions in a certain order. The things or actions can include numbers, letters, words, pictures, procedures, sentences, and mathematical or logical operations.

Criminalists work in a crime laboratory and at crime scenes. The lab is well lighted, ventilated, and clean. Criminalists have office space that includes a desk and computer. Since Criminalists are in contact with physical evidence, they are exposed to disease, chemicals, odors, and fumes. Therefore, Criminalists must wear protective and disposable clothing such as gloves, eyewear, paper suits, and paper shoe coverings when handling body fluid evidence to prevent the transmission of disease. Criminalists are often called to court to provide expert testimony regarding their methods and findings.

Criminalists employed by public agencies are usually included in the union's law enforcement collective bargaining unit. Many unions are local within the public agency whose members they represent. Unions do not usually represent Criminalists who are privately employed.