Decomposition refers to the reduction of the body of a formerly living organism into simpler forms of matter. The body of a living organism begins to decompose shortly after death. Such decomposition can be simplified in two stages: In the first stage, it is limited to the production of vapors. In the second stage, liquid materials form and the flesh or plant matter begins to decompose.

There are environmental influences that will affect decomposition. A body that is exposed to air will decompose more quickly and will have more insect activity. A buried body will decompose eight times slower than a body exposed to air. This is due in part to limited insect activity and possibly lower temperatures. Likewise a body submerged in water decomposes at half the rate of an exposed body. The rate of decomposition depends on the temperature of the water. Cold water will allow slow decomposition and warm water causes faster decomposition. The body is also shielded from insect activity as long as it is submerged.

Forensic art is a law enforcement artistic technique used in the identification, apprehension, or conviction of wanted persons.  Forensic art encompasses several disciplines including composite art, image modification, age progression, post-mortem reconstruction and demonstrative evidence. However, composite art is traditionally the most commonly known discipline of forensic art. The art of composite drawing has been used by police agencies throughout history. When one recalls the Old West, the classic wanted poster with a drawing of a “Bad Guy” comes to mind. These drawings were composites.

Composite Art is an unusual marriage of two unlikely disciplines, police investigative work and art. The cop-artist, almost an oxymoron, possesses both skills. The artist can create a quality facial drawing with assured confidence. Though drawing skills are important parts of composite art, the real challenge is in the ability to interview and relate to a victim or witness. The purpose is to successfully gather, interpret and illustrate the information obtained from the victim’s memory.

In the past twenty years, the discipline of composite art has evolved into forensic art. The forensic artist possesses knowledge of victim psychology, post-mortem reconstruction and human aging. These artists currently use new computer technologies and digital imagery to create more successful investigative images.

Forensic anthropology is the application of the science of physical anthropology and human osteology (the study of the human skeleton) in a legal setting, most often in criminal cases where the victim’s remains are more or less skeletonized. A forensic anthropologist can also assist in the identification of deceased individuals whose remains are decomposed, burned, mutilated or otherwise unrecognizable. The adjective “forensic” refers to the application of this subfield of science to a court of law.

Forensic anthropology borrows methods developed from the academic discipline of physical anthropology and applies them to cases of forensic importance. These techniques can be used to assess age, sex, stature, ancestry, and analyze trauma and disease. Forensic anthropologists frequently work in conjunction with forensic pathologists, odontologists, and homicide investigators to identify a decedent, discover evidence of trauma, and determine the postmortem interval. Though they typically lack the legal authority to declare the official cause of death, their opinions may be taken into consideration by the medical examiner. They may also testify in court as expert witness, though data from some of the techniques commonly used in the field—such as forensic facial reconstruction—are inadmissible as forensic evidence.

Forensic psychology is the intersection between Psychology and the legal system. It is a division of applied psychology concerned with the collection, examination and presentation of psychological evidence for judicial purposes.

The practice of forensic psychology involves understanding applicable law in the relevant jurisdictions in order to be able to make legal evaluations and interact appropriately with judges, attorneys and other legal professionals. An important aspect of forensic psychology is the ability to testify in court, reformulating psychological findings into the legal language of the courtroom to provide information to legal personnel in a way that can be understood. Further, in order to be a credible witness, for example in Canada, the forensic psychologist must understand the philosophy, rules and standards of the American judicial system, as well as display competency in psychological practice. Primary is an understanding of the adversarial model under which the system functions. Lack of a firm grasp of these procedures will result in the forensic psychologist losing credibility in the courtroom.

Forensic toxicology is the use of toxicology and other disciplines such as analytical chemistry, pharmacology and clinical chemistry to aid medicolegal investigation of death, poisoning, and drug use. The primary concern for forensic toxicology is not the legal outcome of the toxicological investigation, but rather the technology and techniques for obtaining and interpreting the results. A toxicological analysis can be done to various kinds of samples.

A forensic toxicologist must consider the context of an investigation, in particular any physical symptoms recorded, and any evidence collected at a crime scene that may narrow the search, such as pill bottles, powders, trace residue, and any available chemicals. Provided with this information and samples with which to work, the forensic toxicologist must determine which toxic substances are present, in what concentrations, and the probable effect of those chemicals on the person.

Determining the substance ingested is often complicated by the body’s natural processes, as it is rare for a chemical to remain in its original form once in the body. For example: heroin is almost immediately metabolized into another substance and further to morphine, making detailed investigation into factors such as injection marks and chemical purity necessary to confirm diagnosis. The substance may also have been diluted by its dispersal through the body; while a pill or other regulated dose of a drug may have grams or milligrams of the active constituent, an individual sample under investigation may only contain micrograms or nano-grams.