135. Forensic biological evidence can usually be analysed for DNA if necessary. DNA analysis in forensic contexts is used to produce profiles that are accepted as identification evidence in many courts worldwide and are individualizing to very high degrees of probability. The persistence of DNA trace evidence depends on the conditions it has endured and the manner in which it is recovered, secured and stored. Damp, humid conditions can affect the persistence of a viable DNA trace and the ability to develop a profile. Evidence should, as far as possible, be maintained at a constant temperature and sealed in such a way as to minimize the risk of contamination. 136. Forensic biological evidence may also be analysed toxicologically for chemicals that have an adverse effect on human beings, such as drugs (controlled substances) and poisons. This applies to biological samples from living persons as well as from the deceased. 3. Non-biological physical evidence i. Chemistry 137. Forensic chemistry is used to identify unknown substances at a crime scene. They include suspected drugs, toxic substances, gunshot residue (firearms) and explosive materials. ii. Firearms 138. Firearms evidence is derived from the examination of handguns and long guns; projectiles such as spent bullets and shot; and ballistic information, including the pattern and movement of projectiles from a firearm after discharge. Trained examiners may be able to link expended projectiles, cartridge casings and related ammunition components to a particular firearm. In addition to matching a particular firearm to a fired projectile or expended cartridge casing, a firearms examiner may also be able to identify the manufacturer of a gun. At the time of drafting of this Protocol, however, toolmark and firearms analysis lacked a precisely defined and universally accepted process.104 104 139. Very often, firearms examiners are also responsible for firearm discharge analysis, to assess whether or not a firearm has been discharged, or analysis of items such as clothing to determine the distance between the impact and the position from which the gun was discharged. Chemical traces on the hands or clothing of a suspect may indicate that he or she has fired a weapon. iii. Fingerprints 140. Fingerprints (including thumb prints) are a long-established means by which persons are individually identified with a high level of probability. This comparison is based on the unique patterns of friction ridges and furrows on fingers and thumbs, as well as on palms, feet and toes. Even identical twins have different fingerprints. Fingerprints are often collected routinely and are a common means of scientific identification. There can be problems, however, for example with partial prints. 141. Fingerprints may be recovered from or visualized on a variety of surfaces (in particular smooth, shiny ones) using a number of techniques. These include applying a powder and “lifting” the fingerprint with a tape or gel lift. Once it has been enhanced with powder, the print can be photographed. It can also be recovered as a complete item and submitted to a laboratory for examination. Latent fingerprints can be visualized on porous surfaces, using a number of chemical enhancement techniques, which are particularly effective on paper. Chemical enhancement is normally undertaken in a laboratory and not at the crime scene, so great care should be taken when packaging and transporting the item. iv. Other non-biological evidence 142. Other relevant evidence includes military ordnance and weapons; fibre analysis; impressions (e.g. tyre tracks, footwear impressions); pattern analysis (e.g. bloodstain patterns/blood spatter analysis, burn patterns, fracture analysis); tool marks; car paint analysis, comparison and identification; and questioned documents. Care needs to be taken to ensure that the analysis of such evidence is underpinned by a validated scientific method. See, e.g., Committee on Identifying the Needs of the Forensic Sciences Community, National Research Council, Strengthening Forensic Science in the United States: A Path Forward, US Department of Justice, Washington, DC, 2009, pp. 150–55, at: http://www.nap.edu/catalog/12589.html. 25