LITMIR.BIZ

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A PoI is found. Fragments of glass are found on their person and measurements of the refractive indices of these fragments are made. These fragments are sometimes known as recovered fragments. Their origin is not known. They may have come from the window broken at the crime scene but need not necessarily have done so.

      The crime scene material is the fragments of glass and the measurements of refractive index of these at the scene of the crime. The suspect material is the fragments of glass found on the PoI and their refractive index measurements.

Evidence where the source is known will be known as source evidence. These fragments of glass will be known as source fragments and the corresponding measurements will be known as source measurements, as their source is known. An alternative term for this type of evidence was bulk source evidence (Stoney 1991a) but this terminology appears to have fallen into disuse.

      A PoI is identified. Fragments of glass are found on their person and measurements of the refractive indices of these fragments are made. Evidence such as this where the evidence has been received and is in particulate form will be known as transferred particle evidence. The fragments of glass in this example will be known as transferred particle fragments. Their origin is not known. They have been received from somewhere by the PoI. They are particles that have been transferred to the PoI from somewhere. They may have come from the window broken at the crime scene but need not necessarily have done so.

      There will also be occasion to refer to the location at which, or the person on which, the evidence was found. Material found at the scene of the crime will be referred to as crime evidence. Material found on the suspect's clothing or in the suspect's natural environment, such as their home, will be referred to as suspect evidence. Note that this does not mean that the evidence itself is of a suspect nature!

Locard's principle (see Section 1.1) is that every contact leaves a trace. In the earlier examples the contact is that of the criminal with the crime scene. In Example 1.1, the trace is the bloodstain at the crime scene. In Example 1.2, the trace is the fragments of glass that would be removed from the crime scene by the criminal (and, later, hopefully, be found on their clothing).

      The evidence in both examples is transfer evidence (see Section 1.1) or sometimes trace evidence. Material has been transferred between the criminal and the scene of the crime. In Example 1.1 blood has been transferred from the criminal to the scene of the crime. In Example 1.2 fragments of glass may have been transferred from the scene of the crime to the criminal. Note that the direction of transfer in these two examples is different. Also, in the first example the blood at the crime scene has been identified as coming from the criminal. Transfer is known to have taken place. In the second example it is not known that glass has been transferred from the scene of the crime to the criminal. The PoI has glass fragments on his clothing but these need not necessarily have come from the scene of the crime. Indeed if the PoI is innocent and has no connection with the crime, the fragments will not have come from the crime scene.

      The term control evidence has been used to indicate the material whose origin is known. Similarly, the term recovered has been used to indicate the material whose origin is unknown.

Alternatively, questioned has been used for ‘recovered’. See, for example, Brown and Cropp (1987). Also Kind et al. (1979) used the word crime for material known to be associated with a crime and questioned for material thought to be associated with a crime. All these terms are ambiguous. The need to distinguish the various objects or persons associated with a crime was pointed out by Stoney (1984).

      Definitions given in the particular context of fibre evidence are provided also by Champod and Taroni (1999). The object or person on which traces have been recovered is defined as the receptor, and the object or person that could be the source (or one of the sources) of the traces, and which is the origin of the material defined as known material, is defined as the known source.

Material will be referred to as control form where appropriate and to recovered or transferred particle form where appropriate. In the previous examples, there are two possibilities for the origin of the material which is taken to be known: the scene of the crime and the PoI. One or other is taken to be known, the other to be unknown. The two sets of material are compared. Two probabilities for what is assumed known are determined. One depends on an assumption of common source. The other depends on an assumption of different sources. The two possibilities for the origin of the material that is taken to be known are called scene‐anchored and suspect‐anchored, where the word ‘anchored’ refers to that which is assumed known (Stoney 1991a). The distinction between scene‐anchoring and suspect‐anchoring is important when determining relevant probabilities (Section 5.3.1.4); it is not so important in the determination of likelihood ratios or Bayes' factors (see Section 2.3.2). Reference to form (source or receptor) is a reference to one of the two parts of the evidence. Reference to anchoring (scene or suspect) is a reference to a perspective for the evaluation of the evidence.

      It is sometimes useful to refer to material found at the scene of a crime as the crime scene item and to material found on or about a PoI as the suspect item. This terminology reflects the site at which the material was found. It does not indicate the kind of material (bulk or transferred particle form) or the perspective (scene – or suspect – anchored) by which the evidence will be evaluated.

      

1.5 Types of Data

A generic name for observations that are made on items of interest, such as bloodstains, refractive indices of glass, etc. is data. There are different types of data and some terminology is required to differentiate amongst them. For example, consider shoe types. The observations of interest are the shoe types as observable on surveillance camera recordings and those observable in possession of a PoI. These shoe types are not quantifiable. There is no numerical significance that may be attached to these. The shoe type is a qualitative characteristic. As such, it is an example of so‐called qualitative data, sometimes known as categorical data. The observation of interest is a quality, the shoe type, which has no numerical significance. The different shoe types are sometime known as categories. The assignation of a shoe to a particular category is called a classification. A shoe may be said to be assigned to one of several categories (see the discussion on the definition of identification in Section 2.5.9). Other examples of categorical data include types of firearms and makes of cars.

      It is not possible to order shoe types and say that one type is larger or smaller than another. However, there are other qualitative data that do have a natural ordering, such as the level of burns on a body. There is not a numerical measure of this but the level of burns may be classified as first, second, third degree, for example. Qualitative data that have no natural ordering are known as nominal data. Qualitative data to which a natural ordering may be attached are known as ordinal data. An ordinal characteristic is one in which there is an underlying order even though it is not quantifiable. Pain is another such characteristic; level of trauma may be ordered as none, slight, mild, severe, or very severe. The simplest case of nominal data arises when an observation may be classified into one of only two possible categories. For example, consider the magnetism of toner present on printed documents. Some toners are magnetic, whereas others are not. Such data are known as binary. Alternatively, the variable of interest, here magnetism, is known as dichotomous; it is either present or absent (Biedermann et al. 2016c).

Other types of data are known as quantitative data. These may be either counts (known as discrete data, since the counts take discrete, integer, values) or measurements (known as continuous data, since the measurements may take any value on a continuous interval).

      A violent crime involving several people, victims and offenders, may result in much blood being spilt and many stains from each of several DNA

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