Transfer evidence is defined as any evidential substance or particle such as blood , fluids , hairs, fibers , paint, and skin that is exchanged between an assailant and the victim or the scene of the crime. Such evidence can transfer either from the criminal to the victim or from the victim to the criminal. It can also be transferred into or out of the crime scene. This transfer often occurs when forcible contact occurs between persons, vehicles, or objects. For example, when glass fragments from one automobile are found on another vehicle, an exchange of transfer evidence has occurred. Different forms of transfer evidence can be small foreign materials such as food particles carried by the perpetrator to the crime scene and left behind, or identifying materials such as the victim's hairs or skin particles carried away from the scene on clothing. Other small particles of transfer evidence may lodge in the hair or under fingernails, or in some other way attach themselves to persons key to the criminal investigation.
An important forensic principle that involves transfer evidence is the Locard's exchange principle . Proposed in 1910 by Dr. Edmond Locard , the principle states that whenever there is contact between two objects (whether either are a living thing or not), there is a transfer of material between them. It is therefore the responsibility of forensic experts to find that transfer evidence, however difficult it may be to locate.
Transfer evidence often plays a critical role in hit-and-run accidents involving a pedestrian hit by a driver. When investigators locate the wrongdoer and his vehicle, it is common to find blood, pieces of clothing, and skin from the victim on the vehicle and pieces of paint or broken glass on the victim that has been transferred from the driver's vehicle.
The principal investigative value of transfer evidence is its ability to be traced. When it is found on a suspect it connects the suspect with the scene of the alleged crime or with the alleged victim. A suspect, who carries away fragments, small materials, or tissues that are clearly identifiable with the victim, can be definitely associated with a particular crime when such transfer evidence is found. Victims who scratch an assailant often lodge minute skin cells, clothing fibers, and other materials from the assailant's body and clothing under their fingernails. These materials can be retrieved by forensic investigators and used as evidence against the alleged criminal.
see also Cast-off blood; Hair analysis; Locard's exchange principle; Paint analysis.