Types of Evidence Used in Forensics

By Douglas P. Lyle

Evidence is anything that can be used to determine whether a crime has been committed. Evidence may link a suspect to a scene, corroborate or refute an alibi or statement, identify a perpetrator or victim, exonerate the innocent, induce a confession, or direct further investigation.

All evidence is not created equal. In fact, evidence is divided into numerous categories depending on its characteristics and reliability. For example, an eyewitness account falls into a different classification than left-behind hair or a piece of clothing.

Direct and circumstantial evidence

Direct evidence establishes a fact. Examples of direct evidence are eyewitness statements and confessions. Circumstantial evidence, on the other hand, requires that a judge and/or jury make an indirect judgment, or inference, about what happened. For example, if a fingerprint or hair found at the crime scene matches that of a suspect, jurors may infer that the print or hair is indeed that of the defendant, and because it was found at the crime scene, links the defendant to the scene.

Physical versus biological evidence

Forensic evidence can be divided into two basic categories: physical and biological. Physical evidence may take the form of nonliving or inorganic items, such as fingerprints, shoe and tire impressions, tool marks, fibers, paint, glass, drugs, firearms, bullets and shell casings, documents, explosives, and petroleum byproducts or distilled fire accelerants. Biological evidence, on the other hand, includes organic things like blood, saliva, urine, semen, hair, and botanical materials, such as wood, plants, pollens and yes, Clarice, moth cocoons.

Reconstructive evidence

Any evidence that helps law enforcement officers better grasp what happened at the crime scene is considered reconstructive evidence. Broken glass or pried-open doors and windows often reveal a perpetrator’s points of entry and exit, and determining whether a window was broken from the inside or the outside tells which way the perpetrator went through it.

Evidence derived from shoeprints, blood spatters, or the trajectory of bullets may pinpoint where in the room everyone was located and exactly how and in what sequence the events of the crime occurred. Whether the victim was attacked from the front or from behind, whether the life was taken quickly or after a struggle, and whether the prime suspect was at the scene at the time of the murder are important aspects in creating a clearer picture of the crime scene.

Another way of looking at reconstructive evidence is that it helps the crime-scene investigator determine who did what, where, when, and how. It may also help determine who is being truthful and who isn’t.

Associative evidence

Associative evidence, in a nutshell, ties a suspect to the crime scene, the victim, or some other bit of evidence. Fingerprints, footprints, hair, fibers, blood and other bodily fluids, knives, bullets, guns, paint, and many other objects and substances, even soil, can link a suspect to the scene.

Associative evidence also can have the opposite effect, proving a suspect’s fingerprints, hair, or blood are not the same as those found at the crime scene, and thus someone else may have committed the crime.