LABORATORY EXAMINATIONS AND ANALYSIS

• Jurisdiction: Australia

Example ........................................................................................................ [88C.700]

The examination of fibres ............................................................................. [88C.720]

Selection of target fibres ............................................................................... [88C.740]

Further examination ...................................................................................... [88C.760]

[88C.700] Example

The following case example is used to illustrate the approach and techniques used in laboratory examinations.

Joan Smith, a 24-year-old single mother, lives in a ground-floor unit. She is in the habit of sleeping in a rear bedroom and does not shut the window. In the early hours of the morning, entry has been gained to her bedroom by cutting open the fly screen on the window. It is alleged that the offender has then threatened the complainant and attempted to have vaginal intercourse before leaving the scene. The offender did not ejaculate. At the time of the alleged assault Joan was wearing a white cotton nightdress which the offender roughly pulled up around her breasts. The bedsheets are a very pale yellow colour and the label indicates the fibre composition to be polyester/cotton. A blue-coloured blanket was also present on the bed. Although the complainant cannot be certain, she thinks the offender was wearing blue denim jeans and a red-coloured windcheater. A suspect has been apprehended within 12 hours of the alleged incident.

[88C.720] The examination of fibres

Figure 3 shows a flow diagram for forensic fibre examination. The search for extraneous fibres is based on the proposition that contact has or has not occurred between the offender and the complainant. The purpose of the examination is to see if there are any fibres which would associate the suspect with the complainant and/or her environment and vice versa.

Figure 3. Flow diagram for forensic fibre examination

The first step is to consider the clothing, bedding and carpets relating to the complainant and the scene from which fibres may have been transferred. These are donor items from known sources.

All of the clothing and bedding is tape-lifted and fully examined for the presence of hairs, stains, damage, etc. Items from the complainant are searched in a separate location from those of the suspect. A series of tape-lifts is thus created for each item. It is important also to collect known fabric/fibre samples from these known items. A small sample of the fabric should be taken. A tape-lift of the surface should also be taken. This serves two purposes, giving an indication of the "shedability" of the fabric (ie, how likely it is that fibres will be shed or transferred) and giving more accurate information about the fibres available on the surface for transfer. With carpets and items which cannot be readily or easily moved, yarns can be cut from the item. As for any known item, the samples must fulfil two criteria: they must be large or adequate enough and they must be representative, that is, include all variation in the item.

The next stage in the examination is to carry out a preliminary study of these known fibre samples. Use is made of both a low magnification stereomicroscope and, where necessary, a compound light microscope with transmitted light and higher magnifications. The author prefers, at this point, to use tape-lifts for the stereomicroscopic examination in the same way as the recovered tape-lifts are later examined.

Table 1 shows the items submitted in this case.

TABLE 1 Items submitted by complainant and suspect

Complainant	Suspect
White, cotton nightdress	Blue, denim jeans
Pale yellow sheets	Red windcheater
Blue blanket	White underpants

Table 2 shows what information is revealed by the preliminary examination.

TABLE 2 Results of preliminary examination

Item	Colour	Fibre description
Cotton nightdress	Microscopically colourless	Twisted or convoluted
Sheets	Almost colourless	Mixture of convoluted cotton fibres and delustered man-made fibres
Blanket	Mid blue	Lightly delustered man-made fibres
Jeans	Pale to dark blue	Short convoluted cotton fibres
Windcheater	Pale and mid red	Pale convoluted cotton fibres and darker delustered man-made fibres
Underpants	Microscopically colourless	Convoluted cotton fibres

[88C.740] Selection of target fibres

With this information target fibres are selected. There are some rules which assist in making this selection. Some types of fibres are not well suited as target fibres. These can be divided into four groups:

(1) fibres which are extremely common or ubiquitous such as colourless cotton and, in most cases, blue cotton fibres from denim fabric. Also, in some situations, work-related clothes will yield fibres which in normal circumstances would be of value but are ubiquitous in the specific case;
(2) garments which are constructed from very smooth, shiny fabrics are unlikely to shed or to retain fibres in any quantities. Shedability can be tested using controlled fabric-to-fabric experiments (De Wael et al, 2010);
(3) fibres which are undyed or those where the dye concentration is so low that the fibres appear to be microscopically colourless; and
(4) fibres from items constructed from shoddy (the term refers to fabric made from reprocessed fibres which are so variable that it is not possible to establish what is a proper known sample).

It cannot be overemphasised that each case has to be assessed on its own merits.

There will be circumstances where colourless or almost colourless fibres can provide useful information. Some discrimination is also possible with blue cotton from denim fabric. In one murder case, large numbers of blue denim cotton fibres were found on the pubic hair of a deceased female. She had not been wearing jeans and although on its own, it was not powerful information, it would have been reasonable to expect that the offender would have had to have been wearing blue jeans. Suzuki et al (2009) have also reported on a fibre simulation which disproved a suspect's confession and provided evidence supporting a different scenario. The suspect was subsequently found guilty of murder.

Gaudette (1988) has also suggested a series of criteria which should be considered at this point in the examination process:

(1) highly shedable garments are difficult and time-consuming to tape but are likely sources of questioned fibres; questioned fibres are those nominated as similar, at the stereomicroscopic level of examination, to known target fibres;
(2) garments of low shedability are good for taping but are not likely sources of questioned fibres;
(3) the more colour contrast there is between the questioned fibres and the garment taped, the better;
(4) fibres that fluoresce under ultraviolet light make good questioned fibres, particularly if the garment to be taped does not fluoresce, or fluoresces to a lesser extent;
(5) the less common the fibre type, the better it is as a questioned fibre;
(6) the darker the fibre, the better it is as a questioned fibre because the chances of a successful microspectrophotometric or dye analysis will be greater;
(7) the coarser the fibre, the more identification and comparison tests can be performed on it; hence the better it is as a questioned fibre;
(8) if a garment is damaged, it is a likely source of questioned fibres; and
(9) special attention should be paid to important areas of the garment as indicated by the circumstances of the case (eg, the seat of a pair of slacks where it is believed that the person was sitting on a seat cover); and
(10) if possible, it is desirable to establish two-way contact or association.

When all of these factors are taken into consideration, it may be that, even if the overall circumstances of the case warrant fibre examination, this may not be possible due to a lack of meaningful target fibres.

In the case scenario, taking these criteria into account, the likely target fibres would be:

• blue man-made fibres - blanket relating to complainant; and
• red cotton and man-made fibres - windcheater relating to suspect.

The next step would be to:

1. search the tape-lifts taken from the items relating to the suspect for blue fibres similar to those constituting the blue blanket; and
2. search the tape-lifts taken from the items relating to the complainant for red fibres similar to those constituting the red windcheater.

Tape-lifts from clothing or other items will have background fibres from the item itself along with a mixture of other fibres picked up over time from contacts the wearer has made. Searching for target fibres is like looking for the proverbial "needle in the haystack". Where fibres are present, a small number will usually be found in a background of up to hundreds of extraneous fibres on a single tape-lift. The analyst should note the presence of any large number of outstanding fibre types and colours. Other than in exceptional circumstances, it is quite impractical, and would serve no useful purpose, to attempt to determine the origin of all the extraneous fibres found to be present.

Fibres similar to the targets are marked on the slide with a permanent marker. These are the questioned fibres. They may be removed by cutting a small window on top of the tape-lift, placing a drop of xylene on the fibre and picking the fibre of interest off with fine forceps: see Figure 4. All of this is done using low magnification microscopy.

Figure 4. The preparation of "questioned" fibres for further examination

Other methods of searching and fibre recovery can be used and some of these are described by Grieve (1990). Some laboratories make use of automated fibre finders. Biermann (1999) describes the strengths and weaknesses of currently available systems. However, the early promise of fibre finders has not been realised and, in...