1
Does the Mark Have Evidential Value?

There are three types of marks that may be found at a crime scene: latent, visible and indented.1

Latent marks are the most commonly encountered and generally require development to make them visible. Latent marks on non-porous surfaces are often developed with powder applied by a brush. The powder will contrast in colour with the surface the mark is on and make the mark visible by adhering to the material it is made in. Once the mark has been developed, it will either be photographed, 'lifted' or both. Lifting involves removing the mark from the surface with adhesive tape. Once the mark is on the tape, the tape is mounted on a backing material to preserve the mark (forming what is known as a 'lift'). Latent marks on porous surfaces such as paper will usually require chemical treatment to make them visible. These treatments are not generally carried out at a crime scene, and so suitable porous surfaces that may bear latent marks will likely be taken to a laboratory. As a laboratory offers a wider range of development techniques than is available at a crime scene, other items or surfaces including non-porous ones may also be taken there to maximise the likelihood of marks being developed.

Visible (or 'patent') marks do not require development because they will usually have been made in a material (such as blood) that contrasts in colour with the surface they are on. Visible marks will usually be recorded by photography.

Indented (or 'plastic') marks are made by impressing the ridges on the skin into a soft material such as putty or clay. Like visible marks, indented marks will usually be recorded by photography.

Whether found at a crime scene or in a laboratory, each mark will be assigned a unique reference. The reference, along with a description of where the mark was located, will be recorded in a report written at the time it was found. Once the scene or laboratory examination is complete, the marks and their accompanying documentation will be sent to the fingerprint laboratory/bureau.

1.1 Continuity and Integrity

Whether a mark has value as evidence in the investigation of an offence and how much value is dependent on several factors.

First, a mark will have no evidential value whatsoever if it is not possible to demonstrate its 'continuity'. From the moment it was found to the moment it was entered as evidence in court, an unbroken chain of custody should exist to demonstrate who has had possession of the mark and when they took possession of it. The organisation that employs the examiner will have procedures that dictate how the mark gets securely from location to location and will have a system to record its movements. The chain will begin with the person who found the mark recording information about the scene the mark was found at and where it was found at that scene. This documentation is crucial in demonstrating that, for example, at some point the mark has not been accidentally or deliberately mixed up with a mark from a different scene or a mark from a different surface at the same scene. How the continuity of a mark can be demonstrated will depend on the procedures of the organisation, but part of it will likely involve making sure that the unique reference assigned to the mark is the same reference that is recorded in the report produced by the person who found it. Additionally, the image of the mark itself may reveal indicators of the surface it was found on, which can be compared to the surface it was reported to have come from. If there is a photograph of the mark in situ on the surface that may conclusively establish where the mark was found but if not, there may also be indicators in a lift that show whether its appearance is consistent with the surface it is reported to have come from. For instance, in addition to revealing the mark, the application of powder to a surface may result in the edges of the surface or indentations and protrusions on the surface being recorded in the lift. The dimensions, shapes and textures of these features can therefore be compared with those of the surface the lift is reported to have come from (Figures 1.1 and 1.2).

Occasionally, as in Figure 1.3, such features may indicate whether the surface they originated from was flat or curved, as may creases in the tape used to lift the mark (Figure 1.4).

Powder may also adhere to contaminants on a surface whose presence may or not be consistent with the surface the mark is reported to have come from (Figures 1.5 and 1.6).

When considering whether the appearance of the lift is consistent with the surface, it must be recognised that some surfaces may appear differently than expected (Figure 1.5). For instance, the surface may be described as wood but depending on its condition, and whether it is painted or varnished, wood grain may or may not appear in a lift from a wooden surface. Also, whilst the use of one type of powder may result in a mark and features of the surface being recorded in the lift, the use of a different type of powder on the same surface may only result in the mark being recorded in the lift. However, the absence of features that may be expected or the presence of those that are not expected may require further investigation as it could indicate the donor of the mark has been wrongly implicated in the offence by a third party (see Appendix 1 on Fabrication, Transplantation and Forgery). This could include examining the original surface or a similar one and lifting marks from it to compare the appearance of those lifts with the original lift.

Figure 1.1 This mark was lifted from the reflective surface of the rear-view mirror of a car. The dimensions of the shape around the mark are consistent with those of a rear-view mirror, as is the appearance of the texture around the edge of the reflective surface. The 'clean' border around the inner side of the textured edge was caused by the lifting tape being unable to contact the point where the plastic frame meets the glass, due to the difference in the height of those surfaces (this has also created unnatural straight edges along the bottom right of the mark). Additionally, the size, ridge flow and orientation of the mark are consistent with it having been made by a left thumb - a digit that could commonly be expected to contact this surface (these indicators are covered in Chapters 6 and 7).

Figure 1.2 This mark was lifted from the painted black surface of an 'L' shaped piece of metal. The mark was developed with silver-coloured powder, and so the image has been inverted to make the ridges appear dark against a lighter background, as they would do in print on a fingerprint form. The edges of the metal can be seen in the lift forming the 'L' shape, and some of the black paint has been lifted off by the tape (the fragments of paint are the irregular shaped white areas). If required, this unique damage to the surface may allow the mark to be married up with a precise point on the surface it came from in the future (assuming the metal is in the same condition it was when the mark was lifted). The dark lines that outline the paint fragments mark the point where the tape rises slightly to accommodate the thickness of the paint. The lines can also be seen around tiny dots throughout the image that are likely small particles of dirt or other debris that were on the surface. The rectangular void near the centre of the mark was caused by recessed damage to the surface.

Figure 1.3 These marks were lifted from a mug. The powder used to develop the marks has also adhered to raised graphics and text on the mug. The marks are adjacent to the top edge of the mug, which appears curved in the lift, as do the horizontal lines that form part of the graphics. This effect is commonly seen when the lifting tape has been wrapped around a curved surface. Additionally, the area of the digits that has contacted the surface and the orientation of the marks is also consistent with the appearance of marks made on this type of surface.

Figure 1.4 This palm mark was lifted from a light bulb. The irregular shape of the mark and the voids running into it are consistent with it coming from this type of surface. The voids are caused by the rectangular tape creasing and folding over on itself as it is applied to a spherical surface.

Figure 1.5 These marks were lifted from the tiled wall of a bathroom. The examiner may expect the appearance of a lift from a smooth and likely clean surface such as this to be relatively featureless. However, in this case, the tiles had been wiped with a wet cloth, and the powder used to develop the ridge detail has also adhered to the dried watermarks left behind by the cloth. The application of powder has also resulted in cracks in the tiles being recorded in the lift as diagonal white lines.

Figure 1.6 This mark was lifted from the outside glass surface of a window. The powder used to develop the ridge detail has also developed some marks left by rain.

The mark may also have no evidential value if it cannot be demonstrated that it is in the same condition it was in when it was found, i.e. that it has not been altered either accidentally or...