Visual identification for species and sex derived from bloodstain based on phosphate-mediated isothermal amplification colorimetric system

Species and sex confirmation of the biological specimen play a crucial role in crime investigation. However, the specimen found in the scene is always trace quantity, which is hard to be analyzed by current methods. Moreover, the time-consuming DNA extraction, sophisticated apparatus, and complex data processing make it difficult to satisfy the demand of speediness and convenience for point-of-care tests. In this study, we first exhibit a phosphate-based visual system for field-based species and sex identification derived from trace bloodstain. By introducing phosphate ion-based colorimetry into loop-mediated isothermal amplification (LAMP) for result interpretation, not only the bloodstain can be directly submitted to mitochondrial variant amplification owing to the enhanced amplification efficiency by pyrophosphate ion hydrolyzation, but also the colorimetric signal can be recognized by the naked eye for result output within 30 min through molybdophosphate generation. Aerosol contamination, the major conflict of LAMP, has been solved once and for all by integrating uracil-DNA glycosylase into this system that still holds on a constant temperature. As a demonstration, cytochrome b and Y-chromosomal amelogenin are employed to identify species and sex respectively, which has achieved a highly sensitive and specific distinguishability under a strong interferential background. Accurate results can be obtained from both the simulative degraded and dated specimen, which indicates that this novel system may serve as a promising tool in forensic practice.

Enhancing forensic investigations: Identifying bloodstains on various substrates through ATR-FTIR spectroscopy combined with machine learning algorithms

The forensic analysis of bloodstains on various substrates plays a crucial role in criminal investigations. This study presents a novel approach for analyzing bloodstains using Attenuated Total Reflectance Fourier Transform Infrared spectroscopy (ATR-FTIR) in combination with machine learning. ATR-FTIR offers non-destructive and non-invasive advantages, requiring minimal sample preparation. By detecting specific chemical bonds in blood components, it enables the differentiation of various body fluids. However, the subjective interpretation of the spectra poses challenges in distinguishing different fluids. To address this, we employ machine learning techniques. Machine learning is extensively used in chemometrics to analyze chemical data, build models, and extract useful information. This includes both unsupervised learning and supervised learning methods, which provide objective characterization and differentiation. The focus of this study was to identify human and porcine blood on substrates using ATR-FTIR spectroscopy. The substrates included paper, plastic, cloth, and wood. Data preprocessing was performed using Principal Component Analysis (PCA) to reduce dimensionality and analyze latent variables. Subsequently, six machine learning algorithms were used to build classification models and compare their performance. These algorithms comprise Partial Least Squares Discriminant Analysis (PLS-DA), Decision Trees (DT), Logistic Regression (LR), Naive Bayes Classifier (NBC), Support Vector Machine (SVM), and Neural Network (NN). The results indicate that the PCA-NN model provides the optimal solution on most substrates. Although ATR-FTIR spectroscopy combined with machine learning effectively identifies bloodstains on substrates, the performance of different identification models still varies based on the type of substrate. The integration of these disciplines enables researchers to harness the power of data-driven approaches for solving complex forensic problems. The objective differentiation of bloodstains using machine learning holds significant implications for criminal investigations. This technique offers a non-destructive, simple, selective, and rapid approach for forensic analysis, thereby assisting forensic scientists and investigators in determining crucial evidence related to bloodstains.

Characterization of insect stains produced by Dermestes maculatus De Greer (Coleoptera: Dermestidae) resulting from interactions with human blood

Insect stains produced by adult Dermestes maculatus were characterized during interactions with human blood. Beetles were offered wet or dried blood positioned on ceramic tiles under laboratory conditions. Despite a life history strategy geared toward consumption of dried food stuffs, adult beetles interacted with wet blood more frequently than dried and produced more insect stains after ingesting wet blood. Most (> 95%) of the insect stains produced were the result of fecal elimination. These stains varied in morphologies but were consistently tan/light, black/grey, or red in color; were round to amorphous in shape; and frequently possessed tails. Tailed stains typically were tadpole-shaped or long and tapering from the stain body, yielding Ltl/Lb ratios greater than 1. Tails were the result of beetle locomotion while defecating. Human blood was detected in defecatory stains when using ABA Hematrace® lateral flow assays. When beetles interacted with dried blood, the bloodstains were most often modified due to physical disruption rather than feeding activity. This yielded flaking or dislodgement of the original stains. Within a forensic context, it is unknown whether D. maculatus interacts with any type of bloodstains at a crime scene.

Establishment of a random forest regression model to estimate the age of bloodstains based on temporal colorimetric analysis

Bloodstain age estimation is important in forensic science. Although several studies have used spectroscopy to estimate bloodstain ages, this method has not yet been practically applied due to the need for expensive equipment and low reproducibility. Thus, we aimed to develop a bloodstain age estimation model that can be easily performed using a spectrophotometric colorimeter. First, bloodstains were prepared by placing blood obtained from five healthy volunteers on a plastic plate. The bloodstains were kept on conditions with various brightness and temperatures. Then, each bloodstain was dissolved in saline every 24 h to a final concentration of 1%, measured with a spectrophotometric colorimeter, and subjected to machine learning to generate a random forest regression (RFR) model, and finally, the prediction accuracy of the bloodstain age was verified. We also elucidated the mechanism of the color changes utilizing aminoguanidine, which is an inhibitor of Maillard reaction. Finally, we measured the time-dependent color changes of the blood fluids obtained from healthy volunteers and examined if the method could be potentially applied to estimate postmortem interval (PMI). Our results showed that the RFR model estimated the bloodstain age with no substantial assessment, and it was applicable to bloodstains, regardless of the brightness or temperature. The color changes were affected by the addition of aminoguanidine. Furthermore, the method could be applied to blood fluids, suggesting its potential usefulness for PMI estimation. Considering its feasibility, the present method could potentially be introduced to practical forensic sciences in the near future.

Quantitative PCR analysis of bloodstains of different ages

An accurate method to estimate the age of a stain or the time since deposition (TsD) would represent an important tool in police investigations for evaluating the true relevance of a stain. In this study, two laboratories reproduced an mRNA-based method for TsD estimation published by another group. The qPCR-based assay includes four transcripts (B2M, LGALS2, CLC, and S100A12) and showed preferential degradation of the 5' end over the 3' end. In this study, the blood-specific marker ALAS2 was added to examine whether it would show the same degradation pattern. Based on our qPCR data several elastic net models with different penalty combinations were created, using training data from the two laboratories separately and combined. Each model was then used to estimate the age of bloodstains from two independent test sets each laboratory had prepared. The elastic net model built on both datasets with training samples up to 320 days old displayed the best prediction performance across all test samples (MAD=18.9 days). There was a substantial difference in the prediction performance for the two laboratories: Restricting TsD to up to 100 days for test data, one laboratory obtained an MAD of 2.0 days when trained on its own data, whereas the other laboratory obtained an MAD of 15 days.

Breaking with trends in forensic dating: A likelihood ratio-based comparison approach

Further steps toward understanding the time-related information contained within bloodstains found at the crime scene are rightly considered a top priority in forensic science. Contrary to widely held assumptions, the reason for the delayed exploitation of bloodstains dating methods in practice is not the lack of suitable analytical techniques for monitoring degradation processes. The problem lies in the variability of the environmental and circumstantial conditions, playing a vital role in the degradation kinetics of blood deposits. The present article demonstrates the possibility of breaking with current approaches based on absolute age estimations to finally answer time-centered questions in real forensic scenarios. The proposed novel framework for situating forensic traces in time is based on the likelihood ratio assessment of the (dis)similarity between the evidence decomposition and sets of reference materials obtained through supervised aging. In such a strategy, every dating procedure is constructed on a case-by-case basis to fit examined blood traces, thereby limiting the adverse influence of external factors on the validity of age estimations and providing a way for future crime scene implementation.

Direct STR profiling from laundered bloodstains: an investigation of different factors of laundering

Bloodstains on fabrics may be washed or cleaned to eliminate incriminating evidence. These actions reduce the chances of obtaining an interpretable DNA profile. Previous studies have shown that conventional short-tandem repeat (STR) typing is affected by various factors associated with washing or laundering of stains. Here, we aim to increase the chances of obtaining interpretable STR profiles from laundered bloodstains using direct PCR. Preliminary investigations showed direct STR typing resulted in more alleles compared to conventional STR typing. We then further investigated the following factors with direct STR typing: fabric type (cotton, polyester, and denim), washing method (hand-washing and machine-washing), type of detergents (powder and liquid), washing temperature (cold to 90 °C), pretreatment agents (sodium hypochlorite and hydrogen peroxide), and the number of washes (one, three, and five). Direct PCR could be successfully used for STR typing from laundered bloodstains with very high success rates. Among the three fabric types, only denim negatively affected direct STR typing, while laundering of bloodstains on cotton and polyester had a negligible effect as mostly full profiles were obtained. Multiple washes resulted in a decrease in both the numbers of alleles and peak heights. Surprisingly, washing method, type of detergent, washing temperature, and pretreatment agents only had minimal to no effect on STR profile quality. Due to the robustness and sensitivity of direct STR typing from laundered bloodstains, the method could be beneficial for violent crime investigations in forensic DNA laboratories worldwide.

Finding blood in the dark: A comparison of infrared imaging devices for the detection of bloodstains on dark fabrics based on their resolution

The use of infrared (IR) light to locate bloodstains on dark fabric is a search technique that is employed in forensic examinations in a number of organisations worldwide. IR is used to complement existing, established visual white light search techniques. There exist a variety of commercially available products that can be purchased for this purpose as well as the option of using IR-converted standard DSLR (Digital Single Lens Reflex) cameras. In this study, a number of IR systems with contrasting resolutions were explored and their performance was assessed on a variety of bloodstain types and fabrics in comparison with white light. The systems ranged from low-budget, low resolution options, such as portable webcams, to vision-industry standard, high resolution, purpose-built cameras for more detailed blood searching of suitable items in the laboratory. Blood spatter, transfer bloodstains, dilute bloodstains, blood mixed with other body fluids and environmental contaminants were among the samples tested on eight different dark fabric types under IR conditions to assess the impact of the resolution differences. All IR systems were able to locate bloodstains, with significantly more bloodstains being found with IR compared to white light. The higher resolution systems were able to locate significantly more bloodstains than the systems with the lower resolution. The webcams were able to locate many of the larger areas of bloodstaining but performed less well in terms of locating smaller bloodstains and dilute blood. False positives such as mud, make-up and brown sauce were detected under IR but were readily discriminated under white light and with presumptive chemical tests. The balance between the ability to locate bloodstains based on system resolution and practicality and possible efficiency gains is discussed.

Differential responses of adult Calliphora vicina to dry bloodstains on porous versus non-porous surface materials

Necrophagous flies are presumed to feed on wet and dried blood at crime scenes, but no empirical information exists detailing fly interactions with dried bloodstains. In the present study, the foraging behavior of adult Calliphora vicina was characterized during interactions with dried bloodstains formed on a variety of porous, and non-porous materials that are commonly encountered in a household. Continuous digital recording and image analysis were used to monitor fly interactions with dried bloodstains and to determine mechanisms of stain modification. Flies displayed differential responses to bloodstains based on the porosity and topography of the surface material. For instance, blood that was not tightly adhered to the materials was flaked or dislodged by fly activity and was not consumed by the flies. On other non-porous surfaces, most stains were consumed following moistening by regurgitation. Feeding activity on such bloodstains frequently yielded partial, perimeter and skeletal stains. In contrast, adult flies rarely mechanically altered dried blood on porous fabrics and there was no evidence of modification due to feeding. Feeding avoidance behavior was observed due to tactile inhibition with blood dried on rough, uneven surfaces like cotton and denim.

The effects of heat on the physical and spectral properties of bloodstains at arson scenes

This study examines the spectral characteristics of blood after being exposed to intense heat within a structural fire. Fire and intense heat have previously been understood to destroy or chemically change bloodstain evidence so that traditional forensic science recovery techniques are rendered ineffectual. Understanding the effects of the denaturation process and physical changes that occur to blood when exposed to heat may develop innovative forensic investigation methods, including the use of reflected infrared photography to enhance the recording of bloodstains. This research revealed that the denaturation of blood, specifically changes to the haemoglobin state from oxyhaemoglobin to methaemoglobin, resulted in the heat affected blood having a more optimal spectral target range within the infrared region when exposed to heat> 200 °C. It was observed both qualitatively and quantitatively using spectrophotometry, that there is a relationship between the appearance, viscosity and infrared absorption properties of blood when exposed to different temperatures as experienced in fire. This result indicated the increased potential for reflected infrared photography to be utilised as an effective tool for crime scene evidence recovery of bloodstains from arson scenes involving fire.

Thermal Effects on DNA Degradation in Blood and Seminal Stains: Forensic View

Forensic investigations using DNA analysis have been grown rapidly. Samples retrieved from crime scene may be exposed to different conditions before proceeding. This study aimed to evaluate the effect of different grades of temperature and burn on DNA extraction and typing.

METHODS

Seven mL of blood and four mL of semen were collected from each volunteer. Effects of temperature grades (100 °C, 50 °C, 37 °C, 4 °C, -20 °C, and burn) on blood and seminal stain were tested.

RESULTS

Bloodstains exposed to temperature grades 100 °C, 50 °C, 37 °C, 4 °C, and -20 °C can be identified using preliminary test while burnt blood stain cannot. Seminal stains exposed to temperature grades 37 °C, 4 °C, and -20 °C can be identified by Florence test while those exposed to 100 °C, 50 °C, and burn cannot. Blood and seminal stains exposed to temperature grades 100 °C, 50 °C, and burn show marked reduction in DNA concentration while maximum DNA conc could be recovered from stains exposed to temperature grade temperature. Both blood and seminal DNA was affected only in case of burn without significant difference between THO1 and Amelogenin primers.

CONCLUSION

High environmental temperature affect the quantity of extracted DNA from different stains but less effect on the quality of extracted DNA. Burn affects both preliminary test, DNA quantity, and quality in stains.

The persistence and stability of miRNA in bloodstained samples under different environmental conditions

miRNA markers have been an area of forensic interest to identify body fluid sources in recent years. In this study, reverse transcription and quantitative real time polymerase chain reaction (RT-qPCR) were performed to detect the existence of blood-specific miRNA markers in bloodstained samples under different environmental conditions, Blood samples from 6 individuals were deposited onto glass plates and exposed to different temperature, humidity, ultraviolet light intensity, and natural condition. When samples were stored to a series of estimated test times, total RNA was extracted and the Ct values of the target RNAs were detected, targets included two miRNA markers (hsa-miR-16-5p, hsa-miR-451a) and one reference gene (U6 snRNA). Analysis results showed that miR-451a represented strong stability and could be detected at all detection points. Meanwhile, each RNAs exhibited unique degradation characteristics, compared to U6, miRNAs showed stronger stability. Additionally, rain had an adverse effect on RNAs stability and accelerates its degradation rate.

The effect of bleaching agents on the DNA analysis of bloodstains on different floor coverings

Blood at crime scenes is one of the most significant traces of evidence in investigation proceedings. Cleaning up these traces with household cleaning products, often containing bleaching agents, inhibits or complicates the detection of DNA. In this study, human blood was applied onto different floor coverings (carpet, laminate, parquet, PVC, tile) and subsequently cleaned with water and bleaching agents (hydrogen peroxide, sodium hypochlorite, DanKlorix®, Vanish Oxi Action®) at different times. Samples have been collected afterwards from the floors. The samples underwent a quantitative and qualitative DNA analysis. Cleaning smooth surfaces with water is usually sufficed to prohibit retrieving a DNA profile in most of the cases. Cleaning carpets was more difficult due to their absorbent surface whereas the use of bleaching agents caused an additional reduction of verifiable DNA concentrations. Retrieving partial or complete profiles after the use of bleaching agents was only possible when cleaning with low concentrations of 3% hydrogen peroxide.

Detection of fly artifacts from four species of necrophagous flies on household materials using immunoassays

An immunoassay was previously developed as a technique to improve methods for detection and analysis of fly artifacts found at crime scenes. The dot blot assay utilized a polyclonal antiserum (anti-md3) based on a unique digestive cathepsin D found in cyclorrhaphous Diptera. In this study, artifacts produced by adults of Calliphora vicina, Cynomya cadaverina, Sarcophaga bullata, and Protophormia terraenovae were examined using the immunoassay to determine if insect-derived stains could be distinguished from a range of human body fluid stains. A lift technique was developed which permitted transfer of fly artifacts from test materials to filter paper for dot blot analyses. All species readily deposited artifacts on all test household materials regardless of diet consumed. Despite differences in texture and porosity of the household materials, artifacts of all species transferred to the filter paper. With all fly species, anti-md3 serum bound to artifacts produced after feeding on semen, blood, feces, urine, and saliva. By contrast, anti-md3 serum did not react with any of the human fluids tested, nor with any of the lifts from household materials not exposed to flies. There was no evidence of false positives with any of the fly species tested, regardless of diet consumed. There was also no indication of false negatives with any of the dot blot assays. These observations suggest that immunoassays using anti-md3 serum performed on a simple lift of suspected fly artifacts can be used effectively as a confirmatory assay to distinguish fly regurgitate and fecal stains from human body fluids.

Immunoassay detection of fly artifacts produced by several species of necrophagous flies following feeding on human blood

Foraging behavior of necrophagous flies commonly leads to distortion of human bloodstains and production of artifacts that confound reconstruction efforts at crime scenes. Currently there is no reliable method for detection of fly-derived stains or distinction of the artifacts from human bloodstains. To overcome these deficiencies, a confirmatory test was developed based on immunological detection of cathepsin D found in digestive fluids of Musca domestica and Protophormia terraenovae. Anti-serum (anti-md3 serum) was generated toward a 17-amino acid synthetic peptide based upon predicted antigenic amino acid sequences for the propeptide and mature enzyme of cathepsin D proteinase from larvae of M. domestica. The serum was used to test the hypothesis that digestive artifacts produced by an array of necrophagous flies associated with human decomposition could be detected with the immunoassay. Anti-md3 serum was able to bind artifacts from 27 species of flies representing 9 families. The antiserum reacted with both regurgitate and defecatory stains, but not transfer patterns. Stains from 4 fly species displayed no reactivity with anti-serum in dot blot assays. Anti-md3 serum did not bind to either human or bovine blood stains on filter paper. However, when both types of blood were spiked with synthetic md3 peptide the antiserum was able to bind. Dot blot assays displayed positive reactions with stains produced from larvae and teneral adults of Sarcophaga bullata, and with artifacts as old as 7-years after deposition. These observations indicate that the immunoassay permits distinction of artifacts from a wide range of species from human bloodstains, from multiple development stages, and from artifacts that remain at crime scenes for many months to years after deposition. Further work is needed to determine whether the detection of fly artifacts using the antiserum is suitable for non-laboratory conditions.

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Antiserum was generated that detects digestive cathepsin D in necrophagous Diptera.

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Anti-md3 serum specifically reacted with regurgitate and defecatory stains produced by flies after consuming human blood.

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The antiserum did not bind human blood or blood from other mammals.

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Anti-md3 shows promise for use in a confirmatory test that reliably distinguishes fly artifacts from human bloodstains.

RNA/DNA co-analysis from bloodstains on aged polyvinyl-alcohol gloves prepared for securing evidence from the hands of victims of fatal gunshot injuries

In contrast to cumulative techniques (e.g., tape-lift) for qualitative gunshot residues (GSR) analysis, topographic methods are commonly applied to preserve the integrity of evidence from a shooter's or victim's hand in cases of gun-related crimes. Topographic sampling techniques employing adhesive foils, latex, or the polyvinyl alcohol (PVAL) method enable unambiguous sampling of biological and non-biological trace material while preserving its spatial distribution and relation to each other. The PVAL method in particular allows for a topographically veridic and quantitative conservation of traces of GSR and biological stains that are embedded in the PVAL glove, because it completely removes these traces from the hand. The present study investigated the success rates of STR profiling and the detection of blood and brain-specific gene expression from minimal traces of blood splatter as well as parallel to the positive detection of gunshot residues embedded in 17 PVAL gloves taken from the hands of deceased persons in the context of homicide cases in the period between 1996 and 2003. The water-soluble PVAL matrix is shown to be fully compatible with successful STR profiling and the detection of blood- and brain-specific miRNA expression, even after up to 20 years of storage, demonstrating that this sampling technique offers advantages compared to other more simplistic sampling methods like taping.

Ascorbic acid and vitamin C-containing beverages delay the leucomalachite green reaction to detect latent bloodstains

The leucomalachite green (LMG) test is one of catalytic tests for the detection of latent bloodstains and generally used in forensic field because of convenience and cost/time-effectiveness. However, contamination of latent bloodstains at crime scenes can interfere with the LMG reaction, resulting in false-negative or false-positive decisions. Herein, we examined if ascorbic acid and vitamin C (l-ascorbic acid or ascorbate)-containing beverages affect the LMG reaction. Ascorbic acid showed the inhibitory activities on the LMG reaction in a dose-dependent manner. Similarly, vitamin C-containing beverages also inhibited the LMG reaction and the inhibitory effects were proportional to the concentrations of vitamin C in beverages. It was also identified that as incubation time after adding LMG reagent to the mixtures of blood and ascorbic acid or beverages was increased, the inhibitory effects of ascorbic acid vitamin C-containing beverages on LMG test were disappeared. These results suggest that the LMG reaction is delayed but not stopped by ascorbic acid and vitamin C-containing beverages. Neither incubation at room temperature around 20-25°C nor the addition of acetic acid affects the inhibitory activity of ascorbic acid on LMG reaction. We also showed that ascorbic acid does not affect DNA stability, allowing us to obtain full short tandem repeat (STR) profiles through amplification of DNA using commercial STR kits. In conclusion, ascorbic acid and vitamin C-containing beverages delayed the LMG reaction, suggesting that it should be considered that negative results of LMG test could be false negative due to contamination of bloodstains with inhibitory factors on LMG test.

A robust background correction algorithm for forensic bloodstain imaging using mean-based contrast adjustment

Background correction algorithm (BCA) is useful in enhancing the visibility of images captured in crime scenes especially those of untreated bloodstains. Successful implementation of BCA requires all the images to have similar brightness which often proves a problem when using automatic exposure setting in a camera. This paper presents an improved background correction algorithm (BCA) that applies mean-based contrast adjustment as a pre-correction step to adjust the mean brightness of images to be similar before implementing BCA. The proposed modification, namely mean-based adaptive BCA (mABCA) was tested on various image samples captured under different illuminations such as 385 nm, 415 nm and 458 nm. We also evaluated mABCA of two wavelengths (415 nm and 458 nm) and three wavelengths (415 nm, 380 nm and 458 nm) in enhancing untreated bloodstains on different surfaces. The proposed mABCA is found to be more robust in processing images captured in different brightness and thus overcomes the main issue faced in the original BCA.

Modified DOP-PCR for improved STR typing of degraded DNA from human skeletal remains and bloodstains

Forensic and ancient DNA samples often are damaged and in limited quantity as a result of exposure to harsh environments and the passage of time. Several strategies have been proposed to address the challenges posed by degraded and low copy templates, including a PCR based whole genome amplification method called degenerate oligonucleotide-primed PCR (DOP-PCR). This study assessed the efficacy of four modified versions of the original DOP-PCR primer that retain at least a portion of the 5' defined sequence and alter the number of bases on the 3' end. The use of each of the four modified primers resulted in improved STR profiles from environmentally-damaged bloodstains, contemporary human skeletal remains, American Civil War era bone samples, and skeletal remains of WWII soldiers over those obtained by previously described DOP-PCR methods and routine STR typing. Additionally, the modified DOP-PCR procedure allows for a larger volume of DNA extract to be used, reducing the need to concentrate the sample and thus mitigating the effects of concurrent concentration of inhibitors.

Systematic investigation of drip stains on apparel fabrics: The effects of prior-laundering, fibre content and fabric structure on final stain appearance

Bloodstain pattern analysis is the investigation of blood deposited at crime scenes and the interpretation of that pattern. The surface that the blood gets deposited onto could distort the appearance of the bloodstain. The interaction of blood and apparel fabrics is in its infancy, but the interaction of liquids and apparel fabrics has been well documented and investigated in the field of textile science (e.g. the processes of wetting and wicking of fluids on fibres, yarns and fabrics). A systematic study on the final appearance of drip stains on torso apparel fabrics (100% cotton plain woven, 100% polyester plain woven, blend of polyester and cotton plain woven and 100% cotton single jersey knit) that had been laundered for six, 26 and 52 cycles prior to testing was investigated in the paper. The relationship between drop velocity (1.66±0.50m/s, 4.07±0.03m/s, 5.34±0.18m/s) and the stain characteristics (parent stain area, axes 1 and 2 and number of satellite stains) for each fabric was examined using analysis of variance. The experimental design and effect of storing blood were investigated on a reference sample, which indicated that the day (up to five days) at which the drops were generated did not affect the bloodstain. The effect of prior-laundering (six, 26 and 52 laundering cycles), fibre content (cotton vs. polyester vs. blend) and fabric structure (plain woven vs. single jersey knit) on the final appearance of the bloodstain were investigated. Distortion in the bloodstains produced on non-laundered fabrics indicated the importance of laundering fabrics to remove finishing treatments before conducting bloodstain experiments. For laundered fabrics, both the cotton fabrics and the blend had a circular to oval stain appearance, while the polyester fabric had a circular appearance with evidence of spread along the warp and weft yarns, which resulted in square-like stains at the lowest drop velocity. A significant (p<0.001) increase in the stain size on laundered blend fabric was identified. Bloodstain characteristics varied due to fibre content (p<0.001) and fabric structure (p<0.001). Blood on polyester fabric, after impact, primarily moved due to capillary force and wicking of the blood along the fibres/yarns, while for the cotton fabrics wicking was accompanied by movement of blood into the fibres/yarns. This study highlights the importance for forensic analysts of apparel evidence to consider the age, the fibre type and the fabric structure before interpreting bloodstain patterns.

Assessment of DNA damage induced by terrestrial UV irradiation of dried bloodstains: forensic implications

Few publications have detailed the nature of DNA damage in contemporary (i.e. non-ancient) dried biological stains. The chief concern, from a forensic standpoint, is that the damage can inhibit polymerase-mediated primer extension, ultimately resulting in DNA typing failure. In the work described here, we analyzed the effects of UVA and UVB irradiation on cell-free solubilized DNA, cell-free dehydrated DNA and dehydrated cellular DNA (from bloodstains). After UV exposure ranging from 25 J cm(-2) to 1236 J cm(-2), we assayed for the presence of bipyrimidine photoproducts (BPPPs), oxidative lesions and strand breaks, correlating the damage with the inhibition of STR profiling. Subsequent to irradiation with either UVA and UVB, the incidence of BPPPs, oxidative products and strand breaks were observed in decreasing quantities as follows: cell-free solubilized DNA>cell-free dehydrated DNA>bloodstain DNA. UVA irradiation did not result in even the partial loss of a STR profile in any sample tested. Somewhat different results were observed after genetic analysis of UVB exposed samples, in that the ability to produce a complete STR profile was affected earliest in bloodstain DNA, next in cell-free solubilized DNA and not at all in cell-free dehydrated DNA. Therefore, it is likely that other types of damage contributed to allele-drop-out in these samples but remained undetected by our assays, whereby the endonucleases did not react with the lesions or the presence of the lesions was masked by strand breaks. Under the conditions of the study, strand breaks appeared to be the predominant types of damage that ultimately resulted in DNA typing failure from physiological stains, although some evidence suggested oxidative damage may have played a role as well.