Statistical evaluation of the evidential value of human hairs possibly coming from multiple sources

A concept of the mathematical evaluation of human hair evidence is derived. This concept can be realized in a special computer program, the output of which is an incrimination probability. The problems of not knowing the true number of sources and the correct partition of hairs corresponding to their sources are solved from the point of view of avoiding an unjustified incrimination.     

The evidential value of black cotton fibres

Forensic scientists are faced with the problem of estimating the frequency of cotton fibres recovered in casework, in relation to those in the general population. One way of doing this is to consider the degree of spectral variation that occurs within a "block of colour". When a spectral pattern occurs very frequently, the evidential value of the fibres may be so low, that it is not worth considering them as target fibres. Using UV-visible range microspectro-photometry (MSP) spectra were recorded from 88 known black cotton dyes and 225 samples of black cotton taken from various textiles. UV-visible spectra originating from sulphur dyes and from the great majority of reactive and direct dyes can be easily recognised. Vat dyes present a little more difficulty. The degree of spectral variation and consequent discriminating power of MSP varied according to the dye class, from 0.13 for sulphur dyes to 0.93 for reactive dyes. From 99 textiles dyed with reactive dyes, the spectra could be divided into at least 40 varieties showing that these fibres have a high degree of individuality. Within the few direct dyes (11.5%) that were encountered, one basic spectral form predominated, but a number of minor variations were observed. Spectral information below 400 nm (UV-range) is important for making distinctions and is critical in the case of direct dyes.     

The evidential value of intra-alveolar haemosiderin-macrophages in cases of sudden infant death syndrome (SIDS)

This study aimed to determine the effect of cocaine on the development and growth of immature and adult blowflies, in an attempt to better understand the impacts of such effects on postmortem interval (PMI) estimation. Twice the lethal dose of cocaine was injected into rabbits. The control animals were injected only with saline solution. Experimental and control rabbits were autopsied, and portions of their livers were exposed to newly eclosed larvae of Chrysomya putoria and Chrysomya albiceps. Larvae were weighed individually every 6 h, up 54 h of exposure. The larvae were then placed on an artificial diet to continue their development. Pupariation time, adult emergence and adult longevity were also analysed. The larvae of both species that fed on the cocaine-containing livers developed faster than those that fed on the livers of the control animals, leading to the conclusion that cocaine influences and stimulates larval growth. The difference in growth between the control and treated flies was best observed from 12 h of exposure onward. This finding has important implications for forensic investigations.     

The evidential value of cosmetic foundation smears in forensic casework

Cosmetic foundation products are easily transferred to clothing and other surfaces as a result of contact with such objects. Examination of past cases involving cosmetics in New Zealand has shown cosmetic foundation to be one of the more common cosmetic products encountered. The aim of this research was to determine the most discriminating method for the comparison of transferred foundation with samples obtained from a known source in forensic casework. Fifty-three foundation samples were analyzed by Fourier transform infrared spectroscopy (FTIR), gas chromatography with a flame ionization detector (GC-FID) and scanning electron microscopy-energy dispersive X-Ray analysis (SEM-EDX). It was found that a 5 mm2 section of a light smearing was enough to provide detectable results. The discriminating powers for FTIR, SEM-EDX and GC-FID were 98.3, 93.8, and 82.0% respectively. A combination of all three techniques provided a discriminating power of 99.7%, meaning that almost complete discrimination was achieved between the foundation samples.     

The evidential value of peptidase A as a semen typing system

Human erythrocyte peptidase A (Pep A) displays a genetic polymorphism in blacks. Its occurrence in human semen was examined for its possible use as a semen typing system. Studies by starch gel electrophoresis, in which the Pep A was located by an improved method, were carried out on semen, semen stains, and vaginal swabs taken at known times after intercourse. In addition, a large number of vaginal swabs, negative for semen, were taken from females throughout their menstrual cycles and examined for Pep A activity. The results indicated that Pep A typing could be carried out on semen and semen stains. However, it was possible to determine the Pep A type on vaginal swabs only when they had been taken within about 3 h after intercourse.     

The evidential value of distorted and rectified digital images in footwear imprint examination

The procedure for forensic photography requires that the film plane be parallel to the taken image. Another procedure must be used when the print is located on reflecting surfaces such as vehicles, or faint marks on porous surfaces. Examination was made of the evidential value of footprint images received from the scene or taken deliberately at an angle out of proper perspective (i.e., the lens axis is not perpendicular to the target plane). An artificial target was prepared and photographed from several lens axis angles ranging from 10 degrees to 85 degrees to the perpendicular, and then rectified using the Adobe Photoshop Version 7.0. It was found that at angles less than 40 degrees , the shape and location of all the individual characteristics were similar enough in comparison to the original image. In images taken at higher angles, the original image could not be adequately restored. The full potential of this image, therefore, could not be achieved after rectification. The results of this study show that the images of a footprint taken at an angle less than 40 degrees , preserve the evidential value of the unique characteristics.     

Suicide with associated acts of arson: two cases from Colorado

We report on two cases of suicide in which the victims started fires before their deaths. In one case the victim died of a single self-inflicted gunshot wound to the head after setting several fires in his residence. In the second case the victim hung himself after setting several fires in his residence and an adjoining building. In both cases, the victim's position was not near the origin of the fires suggesting that the arson was not a failsafe device to the primary mechanism of suicide. Neither victim showed a significant percentage of carboxyhemoglobin, or thermal damage from the fires. Both cases are remarkable in that, had the fire caused more damage to the remains and dwellings, a finding of suicide may not have been reached. We discuss similar aspects between the two reported cases and discuss differences observed with similar events such as complex suicide, suicide by self-immolation, and concealed homicide by burning. Similar cases should be reported to broaden our understanding of these complex events.     

Adhesive tape analysis: establishing the evidential value of specific techniques

This study investigated the evidential value of specific methods of analysis for packaging tapes and clear adhesive tapes available in Australia. Fifty-eight adhesive tapes were analyzed using a wide range of optical, physical, and chemical techniques. The results were collated for the purpose of creating an Australian database of adhesive tapes, which would be of assistance in criminal investigation. Each technique was evaluated for its discriminating power, both for comparative purposes and for the identification of adhesive tapes by comparing unknown samples with the database. The combined discriminating power of the techniques applied is very high. It is possible to individually identify the source of an unknown adhesive tape sample in many instances by searching the database. It is also possible to form an opinion on the significance of a failure-to-discriminate result in comparative casework. Further work is still needed to expand and update the database, as well as compiling data on the relative market share of various products.     

The use of microscopic postmortem changes in anagen hair roots to associate questioned hairs with known hairs and reconstruct events in two murder cases

In two cases investigated by the New Orleans Police Department Crime Lab, hairs recovered from crime scenes were found to exhibit microscopic postmortem changes in anagen hair roots. These microscopic characteristics were used to associate these hairs with various victims in the cases. In addition to associating questioned hairs with known hairs, the fact that the victims were dead when the hairs were pulled helped investigators reconstruct events in both crimes and corroborate statements made by the arrested subjects in each case.     

Fibres used in the construction of car seats — An assessment of evidential value

The evidential significance of car seat fibres has been investigated. Thirty six samples of car seat fabric were examined and the fibres catalogued according to their morphology and characteristics. The majority of car seat fibres were black or grey thick polyester fibres that were either dyed or pigmented. The MSP spectra produced were unlike those usually obtained from black or grey polyester fibres used in clothing. Tapings taken from car seats were examined for car seat fibres, various types were found showing that these fibres are expected to shed from the fabric albeit in low numbers, unless the vehicle is older. No fibres that matched the samples of the car seat fabric were found on the tapings of the car seats. One hundred garments were examined for car seat fibres, 10% of garments had populations of such fibres present and 41% had at least one car seat fibre present. None of these fibres matched the samples of the car seat fabric or those from the car seat tapings.     

Dealing with allelic dropout when reporting the evidential value in DNA relatedness analysis

A method is suggested that allows the use of loci that have shown allelic dropout in kinship analysis as used for disaster victim identification (DVI) and missing person work (MP). This approach uses an extension of a previously published approach to modelling allelic dropout. This method may salvage some information in cases where allelic dropout is hindering DVI or MP work particularly in reconciliations involving a large number of bodies and pedigrees. It should not replace the pursuit of more complete DNA profiles by the normal rework process for such samples.     

A study to investigate the evidential value of blue gel pen inks

The aim of this project was to investigate the evidential value of blue gel pen inks in Europe. For this purpose, 33 blue gel pen inks, of different brands and models, representative of those available on the European market at the time of the study, were analyzed using three techniques: filtered light examination (FLE), Raman Spectroscopy (RS), and scanning electron microscopy (SEM). First, after visual examination (naked eye and stereo microscope), it was possible to classify the 33 inks into three groups described as: milky, metallic, and normal. This paper describes in detail the results obtained for the normal gel pen group. The ability of the techniques to discriminate gel inks between and within brands varied. The results indicated that RS and SEM were more discriminating than FLE. The greatest degree of differentiation was achieved when using a combination of RS and SEM techniques (discriminating power = 0.91). This study also highlights some problems concerning the identification of the brand of a gel pen from a written text.     

Dealing with allelic dropout when reporting the evidential value in DNA relatedness analysis

A method is suggested that allows the use of loci that have shown allelic dropout in kinship analysis as used for disaster victim identification (DVI) and missing person work (MP). This approach uses an extension of a previously published approach to modelling allelic dropout. This method may salvage some information in cases where allelic dropout is hindering DVI or MP work particularly in reconciliations involving a large number of bodies and pedigrees. It should not replace the pursuit of more complete DNA profiles by the normal rework process for such samples.     

A study to investigate the evidential value of blue and black ballpoint pen inks in Australia

The aim of this project was to investigate the evidential value of blue and black ballpoint pen inks in Australia. For this purpose, 49 blue and 42 black ballpoint pen inks, of different brands, models and batches, representative of those ballpoint pens available on the Australian market at the time of the study, were analysed by three techniques: filtered light examination (FLE); reflectance visible microspectrophotometry (MSP); and thin-layer chromatography (TLC). The results showed that the power of the individual techniques to discriminate inks between and within brands, models and batches varied, the most informative techniques being TLC>FLE>MSP. The greatest degree of differentiation was achieved when using a combined sequence of techniques, the discriminating power being 0.99 and close to 1 for blue and black inks, respectively (different brands and models). In respect to the discrimination between different batches of a same brand and model, it was shown that 14 out of the 33 pairs compared could be discriminated. Overall, this study confirmed the high value of the examination of inks when applied to ballpoint pens available in Australia, especially when a combined sequence of techniques is applied.     

Blocks of colour IV: the evidential value of blue and red cotton fibres.

Samples of blue and red cotton fibres were examined using light and fluorescence microscopy as well as UV/VIS microspectrophotometry and fluorescence microspectroscopy. The degree of fluorescence and spectral variation was recorded. Particular attention was paid to the recurrence of certain spectral patterns. The importance of spectral information in the UV range is emphasized again. Colour plays a critical role in the comparison of cotton fibres in forensic sciences. Normally, fibres producing spectral patterns that are frequently seen will tend to have a lower evidential value in criminal cases as the choice of putative sources is theoretically greater and vice versa. Besides black cotton, blue and red cotton fibres are very frequent in fibre casework. The very high discriminating power using a combination of light microscopy, fluorescence microscopy and UV/VIS microspectrophotometry shows that even blue and red cotton fibres can provide excellent evidence when involved in fibre transfer cases.