What are the Different Types of Scientific Evidence Used in Criminal Cases?

Scientific evidence, often referred to as "forensic" evidence, is widely used in the criminal justice system by prosecutors and defense attorneys alike. Whether in a case involving sexual assault, robbery, murder, or other offenses scientific evidence is often used at trial, although that doesn't mean it is always reliable. What are the different types of scientific evidence used in criminal cases not only in Florida but across the U.S.? We'll discuss some of them below.

Forensic evidence including fingerprint ID, DNA matching, and hair or fiber evidence is generally considered scientific evidence before jurors and judges who typically do not have the knowledge and experienced to understand methods used in the development of forensic evidence. In some instances, scientific evidence may even include ballistics, which pertains to guns or other firearms and the bullets fired from those weapons.

DNA analysis or evidence may include biological evidence taken from skin cells, bodily fluids, blood, or even hair. Because DNA or deoxyribonucleic acid is genetic material and differs between every individual who has a unique DNA profile, the results of these tests are said to be more than 99% accurate. The only instance in which more than one person may share a DNA profile is in the case of identical twins. DNA has helped many who have been wrongly convicted of a crime and incarcerated be exonerated and set free; in fact, hundreds have been proven not guilty through post-conviction DNA tests according to the Innocence Project.

Fingerprints have been used to identify people since ancient times, and are the most accurate although you may believe DNA would be the most reliable scientific evidence. Even in the case of identical twins, fingerprints are unique and identifiable by a trained expert. Fingerprints may be taken from a crime scene using powder or chemicals prior to lifting the print, or through ultraviolet lights if the fingerprint is latent. The unique ridges and points found with fingerprints make every individual's prints different.

Hair and fiber evidence. Experts can determine many things from a single hair including whether it is human, the race of the person, hair's color, chemical composition, presence of toxins, and more. For the most part hair evidence is used to exclude someone suspected of a crime, as the only way to know for absolute certain a hair found at a crime scene is the suspect's is if the root or follicle is attached, which can be DNA tested. For example, if the suspect is a Caucasian with brown curly hair and the hair in question is determined by experts to be that of an Hispanic person and is straight or black, it cannot be the hair of the suspect.

Fibers may originate from carpeting, fabric, upholstery, curtains, even clothing. Classified as either natural, synthetic, or manufactured, fibers are often useful to those investigating a crime scene due to the fact the origin of the fiber may be identified. A suspect may have a fiber from a victim's clothing on his or her own clothing, a carpet fiber on his or her shoe, etc.

Ballistics is considered scientific or forensic evidence by some, although many criminal defense attorneys consider it "junk science" as the reliability of the evidence can be in question. Ballistics are often used by investigators to determine the type of weapon used to commit a crime, the shooter's location based on the angle of trajectory of the bullet, the "rifling" of a spent bullet (marks made on the bullet while passing through the barrel) which can help determine the type of weapon used, and more.

Scientific evidence has proven extremely useful in criminal cases for both defense lawyers and prosecutors. However, it is important to keep in mind that errors can be made with any type of evidence. For instance, DNA evidence may be contaminated or compromised due to improper collection or handling. With every type of evidence whether forensic or circumstantial, there can be issues that leave questions in the mind of jurors. Even in criminal law cases, nothing is foolproof.

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