Physical evidence encompasses any and all objects that can establish that a crime has been committed or can provide a link between a crime and its victim or a crime and its perpetrator.
Physical evidence also does not have to be a tangible substance. It can also be a print or pattern left at the scene. Trace evidence refers to evidence in very small amounts, which may be easily overlooked or lost if not looked for carefully and with the correct techniques employed.Examples of physical evidence includes:-
- A human body or its parts.
- Body trace evidence:fluids such as blood, semen, urine, stool, sweat and saliva, body tissues and hair.
- From clothing and other attachments applied to or worn on the body.
- Questioned documents.
- Illicit drugs and controlled chemical substances.
- Fire and chemical residues in cases or arson, including petroleum products.
- Explosive residues and casing of detonators, etc., in cases of bombings.
- Fabrics (clothing and coverings) and fibres.
- Prints and Impressions: Fingerprints, sole prints, tyre prints, etc.
- Firearms and Ammunition.
- Powder residues, glass, paints and plastics.
- Soils, elemental analysis / mineralogy and metallurgy.
- Tool marks and Serial numbers.
- Vehicle Lights and Glass parts.
- Wood, pollen and other vegetative matter, incl. debris and other foreign materials in wounds and clothing.
- Adhesives and dyes.
- Ropes and cords.
- Audio-visual / electronic devices/computers.
The Value of Physical Evidence:-
- Defining the elements of the crime. Such as the identification and quantification of a drug or controlled substance or the determination of the quantity of alcohol in the blood of a person suspected of driving while intoxicated.
- Providing investigative leads for a case. An example of this would be the identification of a vehicle type in a hit-and-run case through automotive paint and glass analysis.
- Linking a crime scene or a victim to a suspect. This like may be provided through analysis of various types of physical evidence such as hair, blood, semen, and fingerprints.
- Corroborating or refuting a suspect’s statement of alibi. In a fatal gunshot case, the examination of bloodstained patterns at the scene and on a suspects clothing may establish whether a victim was struggling with an assailant as may be claimed or conversely show that the victim was in a totally different position or location when the shot was fired.
- Identifying a suspect. The identification of a suspect is not limited to but often established through fingerprint comparison or DNA profiling.
- Inducing a confession of a suspect. In some cases presenting factual information to a suspect established through the examination of physical evidence, such as the victim’s blood identified on their clothing of fingerprints identified on a weapon, will encourage the person to admit involvement in a crime.
- Exonerating the innocent. Physical evidence may be found that may prove a person did not commit a crime. This is often referred to as exculpatory evidence.
- Providing expert testimony in court. The presentation of physical evidence in court by an expert is the ultimate test of the validity of the evidence.
The Functions of the Forensic Scientist and the Forensic Laboratory:-
- Analysis of physical evidence.
- Provision of expert testimony.
- Furnishing training in the proper recognition, collection, and preservation of physical evidence.