Illuminating the benefits and limitations of forensic light sources.

Forensic light sources, such as a Crime-lite, are used in forensic laboratories and by police staff in the examination for, and detection of, biological material. Whilst the benefits of using forensic light sources are relatively well understood, their limitations are less-so. This report details the outcome of studies, validation and review by three forensic laboratories, as well as three case examples, to highlight both the strengths and weaknesses of the tested forensic light sources and to demonstrate that, whilst a useful preliminary screening tool, they should not be used in isolation without subsequent presumptive chemical testing. False positives and negatives are common, and the background substrate and specific biological material present can have a significant effect on the outcome of examination when using a forensic light source.

Evaluation of the relationship between the detectability of seminal stains on laundered fabric and stain age.

In some cases of sexual assault that are not reported to judicial authorities within a certain time, it is important to detect and identify seminal stains on laundered fabrics. In this study, we aimed to reveal the effect of the time from staining to laundering on the detectability and identification of seminal stains on laundered clothes. A total of 180 pieces of fabric (four different colours and five different types) were stained with seminal fluids, and three different lag times (12 hours, 1 week and 1 month) from staining to laundering were used. Three different laundering protocols were applied to these fabrics after staining. The built-in camera of the Mobile Multispectral UV-VIS-IR Imaging System® was used to take photos (1260 in total) of the stains with seven different wavelength and filter options, and the obtained images were evaluated. The Seratec® PSA Semiquant test was used to analyse the presence of prostate-specific antigen (PSA) in the seminal stains laundered after different lag times. We observed that in examining with the forensic light source (FLS) system, the time from staining to laundering affected the detectability of seminal stains on pieces of cloth. The best fluorescence was obtained in the examination of semen-stained fabric with FLS, particularly when the fabric was not laundered for one month after staining. On the other hand, the time from staining to laundering had a more limited effect on PSA test positivity than on the results of the examination with FLS.

Beneath cover-up tattoos: possibilities and limitations of various photographic techniques.

BACKGROUND: The goal of this study was to investigate the usefulness of various photographic techniques in visualizing previous tattoos under cover-up tattoos. MATERIAL AND METHODS: Ten volunteers with 11 known cover-up tattoos were examined using different photographic techniques: A Canon EOS 6D full-frame digital single-lens reflex camera used in conjunction with a SB600 off-camera flash system and an extension cord; and a Leica M8 digital imaging system camera in conjunction with two different infrared filters (715 nm and 850 nm) and a Metz CL-45 handle-mount flash. A Lumatec Superlite 400 forensic light source was used along with the Canon EOS 6D as a third system. RESULTS: The best results for black cover-up tattoos were achieved with the full-frame digital single-lens reflex camera in conjunction with the off-camera flash system and, for colored cover-up tattoos, with IR-photography at a wavelength of 850 nm. The Lumatec Superlite 400 light source did not provide better results for conventional photography than those obtained with flash lighting. DISCUSSION: In nine out of eleven cover-up tattoos, the previous tattoos could, at least, be partially visualized. The quality of the visualization depended on the color, pattern, density, and quality of the cover-up tattoo as well as on the photographic technique. None of the examined photographic techniques could satisfactorily image the previous tattoo if the cover-up tattoo was large and black, especially not if it was densely inked. CONCLUSION: Depending on the color of the cover-up tattoo, a full-frame digital single-lens reflex camera in conjunction with a SB600 off-camera flash system (for black cover-ups) or infrared photography with flash lighting and an 850 nm filter (for colored cover-ups) proved to be the best of the investigated techniques to visualize a previous tattoo under a cover-up tattoo.

Is the visibility of standardized inflicted bruises improved by using an alternate ('forensic') light source?

AIM: To study the visibility of standardized inflicted bruises by using an alternate ('forensic') light source compared to a white light source. METHODS: Bruises were inflicted on the flexor site of the forearm (halfway in the middle) in 76 adults, by suddenly allowing a cylindrical metal object (400g) with rounded edges to drop for 1m in a vertically positioned tube. At 0.25, 1, 2, 7 and 14days after this blunt force impact, the impact site on the forearm was photographed with a white light source and subsequently with an alternate light source at 415nm. Visibility of bruises on 170 randomized photographs was assessed on a calibrated monitor by 10 forensic medical specialists (physicians and pathologists) independently in two sessions: (1) with white light source photographs, and (2) after a mean of 11days with greyscale converted alternate light source photographs. Bruise visibility was expressed as a report mark between 1 (very bad) and 10 (excellent), or as 'no visible bruise'. To determine intra-rater agreement, 10 of 170 photographs were assessed twice (untold to the assessors). In total 3600 (180×10×2) photographs were assessed. RESULTS: 39 of 73 (53%) participants who completed the study, developed a visible bruise (women more often than men, p<0.001). Inter-rater agreement between assessors was high (mean inter-class coefficient, ICC, for white light source 0.66 (SD 0.14) and for alternate light source ICC 0.73 (0.09)). Intra-rater agreement was excellent (mean ICC 0.88 (SD 0.09)). Mean report marks for bruise visibility, recorded independently by 10 assessors on 170 unique photographs per light source, were significantly higher with an alternate light source than with a white light source, at 1 and 2days after impact: 4.4 (SD 2.0) vs 3.8 (1.8) (p<0.01) and 4.9 (2.1) vs 4.5 (2.0) (p<0.05), respectively. However, these differences were small, as the mean difference (effect size) in report marks were 0.6 (0.5) and 0.4 (0.3), at 1 and 2days after impact, respectively. The other time points showed no statistical significant differences in report marks. CONCLUSIONS: Bruises after standardized blunt force impact were slightly better visible with an alternate light source than with a white light source after 1 and 2 days, but not after 0.25, 7 and 14 days. The value of using an alternate light source at 415nm to improve bruise visibility was limited in this study.

Gunshot residue on dark materials: a comparison between infrared photography and the use of an alternative light source.

The pattern of gunshot residue (GSR) includes important information about muzzle-target distance since a larger GSR distribution diameter indicates a larger shooting distance. GSR may not be visible to the naked eye when, for example, it is located on dark textiles. In such cases, further procedures need to be performed in order to visualize the pattern of GSR. Besides chemical procedures, an alternative light source or infrared photography can be utilized for non-destructive GSR visualization. In the work presented, these two techniques are compared based on shooting experiments using 26 different dark textiles. Within the range of the alternative light source, the use of a 440-nm light in combination with an orange-colored filter led to the best visualization of GSR in the form of fluorescent particles. Infrared photography, on the other hand, visualized GSR as dark particles, whereas-ideally-the dark textile reflected the infrared light and appeared bright. The comparison of both techniques revealed that the GSR distribution visualized by infrared photography was not identical to the GSR distribution visualized with 440-nm illumination in combination with an orange-colored filter. We concluded that infrared photography visualizes the inner powder soot zone, whereas illumination at 440 nm leads to fluorescence of the outer powder soot zone, which can be visualized using an orange-colored filter. Knowledge of this difference in visualization of the two powder soot zones is important for forensic practitioners assessing firing distances. In the literature, however, this difference is not noted as clearly.

Detection of painted-over traces of blood and seminal fluid.

Dealing with a refurbished crime scene is a special challenge for forensic investigators. In such cases, a crime scene may not have only been cleaned in order to erase all traces but the walls of an indoor crime scene could also be painted over in order to mask traces of the crime. So far, very few publications have shown that painted-over traces of blood and seminal fluid can be detected using a forensic light source or infrared photography. To date, there have been no systematically executed research studies including guidelines on which settings to use depending on the color of the wall. Moreover, no comparative study has addressed the question of whether it is better to use infrared photography or a forensic light source to visualize painted-over bloodstains. The present study covers the aforementioned gaps and shows that painted-over bloodstains are most easily visualized by infrared photography, while traces of seminal fluid are most easily visualized at 440 nm in combination with a yellow filter-both independent of the color of the wall paint.

Estimating the postmortem interval of human skeletal remains by analyzing their fluorescence at 365 and 490 nm.

The study presented here is regarded as a continuation of the experiments of Sterzik et al., who developed a new practical method to distinguish between historical and recent human skeletal remains. Bone cross-sections were illuminated using light with wavelengths of 365 and 490 nm, causing fluorescence. The fluorescence was documented by photography and further analyzed to examine the areal extent of a certain fluorescent color. Contrary to the previous experiments of Sterzik et al., the present study focused on bones with postmortem intervals (PMIs) ≥ 50 years. Therefore, this study fills the gap created by the former study, pointing towards a correlation between the PMI and the areal extent of the fluorescent surface in both tests. The presence of blue and red fluorescent surfaces < 1% indicated a PMI ≥ 50 years. Furthermore, the presence of blue and red fluorescent surfaces > 1% can be regarded as a marker to exclude a PMI ≥ 50 years; in fact, these bones are likely to have a PMI < 30 years.

Visualizing old biological traces on different materials without using chemicals.

During the investigative process that typically follows a criminal act, it may prove necessary to work with and analyze evidence that is not recent but old. This could become necessary, for example, when a crime is discovered some time after it was committed or when a cold case is reopened. Due to this need, the present study focused on the detection and visualization of 2-year-old biological traces. To do so, an alternative light source and different filters were used. The optical behavior of 2-year-old samples of blood, semen, urine, saliva, and sweat located on 19 different materials was documented, analyzed, and compared with the optical behavior of the same samples when they were recent [1].

Estimating the postmortem interval of human skeletal remains by analyzing their optical behavior.

The aim of this study was to figure out a new practically applicable method to distinguish between historical and recent human skeletal remains. Therefore, the optical behavior of bone cross sections was investigated using the combination of two methods: a modification of an already established test (UV-induced fluorescence) and a new method (490 nm-induced fluorescence). We evaluated the areal extent of fluorescence of 30 bone cross sections with known postmortem interval (PMI) using ultraviolet light and 490 nm light. For analysis, the areal extend of fluorescent surface was determined using photos of the samples and an image editing software. The results prove that there is a correlation between PMI and the areal extent of fluorescent surface in both tests. Furthermore, the combination of both methods is a good indicator to distinguish within the forensic relevant post mortem interval between PMI < 30 years and PMI > 30 years.

Visualisation of latent fingermarks on polymer banknotes using copper vacuum metal deposition: A preliminary study.

The UK's recent move to polymer banknotes has seen some of the currently used fingermark enhancement techniques for currency potentially become redundant, due to the surface characteristics of the polymer substrates. Possessing a non-porous surface with some semi-porous properties, alternate processes are required for polymer banknotes. This preliminary investigation explored the recovery of fingermarks from polymer notes via vacuum metal deposition using elemental copper. The study successfully demonstrated that fresh latent fingermarks, from an individual donor, could be clearly developed and imaged in the near infrared. By varying the deposition thickness of the copper, the contrast between the fingermark minutiae and the substrate could be readily optimised. Where the deposition thickness was thin enough to be visually indistinguishable, forensic gelatin lifters could be used to lift the fingermarks. These lifts could then be treated with rubeanic acid to produce a visually distinguishable mark. The technique has shown enough promise that it could be effectively utilised on other semi- and non-porous substrates.

Searching for biological traces on different materials using a forensic light source and infrared photography.

Because biological traces often play an important role in the investigation process of criminal acts, their detection is essential. As they are not always visible to the human eye, tools like a forensic light source or infrared photography can be used. The intention of the study presented was to give advice how to visualize biological traces best. Which wavelengths and/or filters give the best results for different traces on different fabrics of different colors? Therefore, blood (undiluted and diluted), semen, urine, saliva, and perspiration have been examined on 29 different materials.