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Class and Individual Characteristics

Home > Evidence Handling Procedures > Types of Evidence > Class and Individual Characteristics

All evidence bears class characteristicsIndividual characteristics may or may not be present.

Evidence that possesses class characteristics may be referred to as class evidence. Similarly, evidence that possesses individual characteristics may be referred to as individual evidence.

Both class and individual evidence have value; however, it typically takes considerably more class evidence (and time for collection and analysis) to have the same weight and significance as a single item of individual evidence.

Criminal cases based solely on class evidence are more difficult to prove and require more work, but the results can be just as significant. To put it in perspective, in terms of probative value in the courtroom, it usually takes a considerable combination of class evidence to equate to a single item of individual evidence.

Class and Individual Characteristics
Characteristic Definition Examples
Class Characteristics

Measurable features of an item that indicate a restricted group source based on design factors determined prior to manufacture

May be shown to be like or consistent with a questioned source, although not uniquely identifiable with that source

  1. Width of the tip of a screwdriver
  2. Width of land and groove impressions
  3. Close-up examination of fired bullet under a microscope.

    Example of lands and grooves

  4. Bloodstain
Subclass Characteristics

Discernible surface features of an object, more restrictive than class characteristics

Produced incidental to manufacture

Refer to a smaller group source (a subset of the class to which they belong)

May arise from a source that changes over time

  1. Marks on an object produced by a grinding wheel or sanding belt.
  2. Manufacturing marks on a group of Ruger firearms
  3. Close-up examination of marks and gouges on a metal surface.

    Manufacturing marks on a
    group of Ruger firearms

    Greg Scala, FDLE, Orlando, FL

  4. Blood type
Individual Characteristics

Marks on an object produced by the random imperfections or irregularities on the surfaces of the tools used to manufacture the object

Produced incidental to the manufacturing process and typically seen at microscopic level

Can be produced on an object by use, abuse, and/or corrosion

May be uniquely identifiable with a source

  1. Striated and/or impressed marks produced by the action of the tip of a screwdriver on an object
  2. Striation marks on a fired bullet
  3. Close-up examination of parallel marks on the side of a fired bullet.

    Striation marks on a fired bullet

  4. DNA profile from a bloodstain

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