Types of evidence

TYPES OF EVIDENCE

• Evidence can be categorized into various types, with physical evidence being one of the most critical in forensic investigations.

COMMON TYPES OF PHYSICAL EVIDENCE

• Almost anything can serve as physical evidence in a criminal case.

• Key examples of physical evidence include:

  • Biological Evidence:

    • Blood: Can be in liquid or dried form. Identifiable through serological or biochemical analysis to ascertain its origin.

    • Semen & Saliva: Also available in liquid or dried form and similarly analyzed for origin identification.

FURTHER SPECIFICATIONS OF PHYSICAL EVIDENCE

• Documents:

  • Can be used to authenticate handwriting and examine materials such as paper and ink.

• Drugs:

  • Evidence concerning the sale, manufacture, and use of drugs can be critical in investigations.

• Explosives:

  • Includes devices with explosive charges and items that contain residue from explosive materials.

• Fibers:

  • Fibers can be natural or synthetic and often transfer between individuals or objects, supporting Locard’s principle of exchange.

• Fingerprints:

  • Can be visible or latent (hidden) and serve as a reliable means of identification.

• Firearms and Ammunition:

  • Includes both intact and discharged ammunition, which can connect a suspect to a crime.

• Glass:

  • Glass particles may be collected from crime scenes, especially relevant in cases of gunfire (e.g., windowpanes).

• Hair:

  • Can be identified as animal or human hair, providing crucial information.

• Impressions:

  • Include tire marks, shoe prints, bite marks, and fabric impressions; can reveal important details about a crime.

• Paint:

  • Can be liquid or dried and may connect items transferred during a crime.

• Petroleum:

  • Commonly related to arson, for instance, gasoline residue.

• Powder Residues:

  • These are collected from firearms, indicating discharge during criminal activity.

• Soil:

  • Soil can embed in shoes and can offer links to a specific location.

• Tool Marks:

  • Impressions left by tools during a crime, like crowbars or screwdrivers.

• Wood or Vegetative Matter:

  • Items such as sawdust or plant material found on clothing or tools can be relevant.

EXAMINATION OF PHYSICAL EVIDENCE

• Purpose:

  • Physical evidence is examined primarily for identification and comparison to support criminal investigations.

• Identification Process:

  • Determining the physical or chemical identity of substances, e.g., composition of illicit drugs or explosives.

  • Species Origin:

    • Identifying the origin of biological material (blood, hair, semen) is critical for establishing connections.

• Comparison Procedures:

  • Ascertaining whether two or more objects have a common origin, such as hair or paint samples. This process can affirm connections between suspects and crime scenes.

• Individual Characteristics:

  • Evidence with high probability association to a common source, including:

    • Fingerprint ridges

    • Bullet striations

    • Handwriting characteristics

    • Footwear impressions

• Class Characteristics:

  • Evidence that is associated with a group rather than a single source, for instance, car paint or fabric fibers.

CURRENT WEAKNESSES IN FORENSIC SCIENCE

• Limitations of Class Evidence:

  • A notable challenge is the difficulty in assigning exact probability values to class evidence comparison, affecting link determinations:

    • The difficulty in determining whether a specific fiber originated from a particular item (e.g., sweater).

    • Linking paint chips to a specific car in incidents like hit-and-run events.

• Most forms of physical evidence from crime scenes struggle to pinpoint a definitive single source.

• Increasing connections between various evidence types can affirm an individual's involvement, whereas differing findings can exonerate suspects from claims.

FORENSIC DATABASES

• IAFIS:

  • Integrated Automated Fingerprint Identification System, managed by the FBI, for maintaining fingerprints and criminal histories.

• CODIS:

  • Combined DNA Index System allows for the electronic exchange and comparison of DNA profiles at various jurisdictional levels.

• NIBIN:

  • National Integrated Ballistics Information Network for analyzing firearm markings on bullets and cartridge casings.

• PDQ:

  • International Forensic Automotive Paint Data Query database, containing paint data.

• SICAR:

  • Shoeprint Image Capture And Retrieval database focusing on shoe prints.