Surface-sampling and analysis of TATP by swabbing and gas chromatography/mass spectrometry

The method of sample recovery for trace detection and identification of explosives plays a critical role in several criminal investigations. After bombing, there can be difficulties in sending big objects to a laboratory for analysis. Traces can also be searched for on large surfaces, on hands of suspects or on surfaces where the explosive was placed during preparatory phases (e.g. places where an IED was assembled, vehicles used for transportation, etc.).In this work, triacetone triperoxide (TATP) was synthesized from commercial precursors following reported methods. Several portions of about 6 mg of TATP were then spread on different surfaces (e.g. floors, tables, etc.) or used in handling tests. Three different swabbing systems were used: a commercial swab, pre-wetted with propan-2-ol (isopropanol) and water (7:3), dry paper swabs, and cotton swabs wetted with propan-2-ol. Paper and commercial swabs were also used to sample a metal plate, where a small charge of about 4 g of TATP was detonated. Swabs were sealed in small glass jars with screw caps and Parafilm^® M and sent to the laboratory for analysis. Swabs were extracted and analysed several weeks later by gas chromatography/mass spectrometry. All the three systems gave positive results, but wetted swabs collected higher amounts of TATP. The developed procedure showed its suitability for use in real cases, allowing TATP detection in several simulations, including a situation in which people wash their hands after handling the explosive.     

Recovery of human DNA profiles from poached deer remains part 2: Improved recovery protocol without the need for LCN analysis

Although poaching is a common wildlife crime, the high and prohibitive cost of specialised animal testing means that many cases are left un-investigated. We previously described a novel approach to wildlife crime investigation that looked at the identification of human DNA on poached animal remains (Tobe, Govan and Welch, 2011). Human DNA was successfully isolated and amplified from simulated poaching incidents, however a low template protocol was required which made this method unsuitable for use in many laboratories. We now report on an optimised recovery and amplification protocol which removes the need for low template analysis.Samples from 10 deer (40 samples total — one from each leg) analysed in the original study were re-analysed in the current study with an additional 11 deer samples. Four samples analysed using Chelex did not show any results and a new method was devised whereby the available DNA was concentrated. By combining the DNA extracts from all tapings of the same deer remains followed by concentration, the recovered quantity of human DNA was found to be 29.5 pg ± 43.2 pg, 31 × greater than the previous study. The use of the Investigator Decaplex SE (QIAGEN) STR kit provided better results in the form of more complete profiles than did the AmpF?STR® SGM Plus® kit at 30 cycles (Applied Biosystems). Re-analysis of the samples from the initial study using the new, optimised protocol resulted in an average increase of 18% of recovered alleles. Over 17 samples, 71% of the samples analysed using the optimised protocol showed sufficient amplification for comparison to a reference profile and gave match probabilities ranging from 7.7690 × 10^? 05 to 2.2706 × 10^? 14.The removal of low template analysis means this optimised method provides evidence of high probative value and is suitable for immediate use in forensic laboratories. All methods and techniques used are standard and are compatible with current SOPs. As no high cost non-human DNA analysis is required the overall process is no more expensive than the investigation of other volume crime samples. The technique is suitable for immediate use in poaching incidents.     

Duplex-specific nuclease (DSN): A method for the rehabilitation of low-copy number DNA profiles

A continual challenge in the field of forensic DNA analysis is the amplification and interpretation of degraded and low-copy number (LCN) DNA obtained from amounts of limited biological evidence. It has been well established that DNA profiles obtained from the amplification of low quality, degraded, and/or LCN DNA samples are often of limited value due to the frequent occurrence of preferential amplification during polymerase chain reaction (PCR). The by-products of preferential PCR amplification are often observed as inter- and intra-locus peak imbalance, allelic dropout, and/or locus dropout. These are all artifacts that are identified during the interpretation phase of analysis rather than by improving the quality of the DNA present. While it is theoretically possible to obtain a complete DNA profile from a single cell, in reality, profiles obtained from suboptimal amounts of DNA are difficult to interpret and frequently inconsistent when replicated. Inspired by advances in next-generation sequencing techniques, we propose a methodology for simultaneously normalizing the abundance of PCR products across all short tandem repeat (STR) loci using the DNA exonuclease, duplex-specific nuclease (DSN). DSN is an enzyme isolated from the hepatopancreas of Red King (Kamchatka) crab that possesses a strong affinity for digesting double stranded DNA (dsDNA) and has limited activity toward single stranded DNA (ssDNA). Degraded DNA known to display peak imbalance and allele dropout was amplified using AmpFlSTR^® Identifiler^® Plus for 28 cycles. Following amplification, samples were denatured at 99.9 °C for 5 min and incubated with one unit of DSN at 62 °C in a 28 μl volume for 1 min. Nuclease activity was terminated through the addition of equal volume of 10 mM EDTA and 95 °C incubation for 2 min. Following DSN treatment, 21 of 30 alleles within the known profile exhibited some improvement in peak height balance. The findings obtained support the potential use of DSN treatment as a method for normalizing STR profiles and improving the quality of data from degraded and low quantity DNA samples.     

Characterisation of forward stutter in the AmpFlSTR® SGM Plus® PCR

PCR amplification of tetrameric short tandem repeats (STRs) can lead to Taq enzyme slippage and artefact products typically one repeat unit less in size than the parent STR. These back stutter or n ? 4 amplification products are low-level relative to the amplification of the parent STR but are widely seen in the forensic community where tetrameric STRs are employed in the generation of DNA profiles. To aid the interpretation of DNA mixtures where minor contributor(s) might be present in comparable amounts to the back stutter products, the typical amounts of back stutter generated have been well characterised and guidelines for interpretation are in place. However, further artefacts thought to be Taq enzyme slippage leading to products with one repeat unit greater than the parent sequence (n + 4 or forward stutter) or two repeats less (n ? 8 or double back stutter) also occur, but these have not been well characterised despite their potential influence in mixture interpretations. Here we present findings with respect to these additional artefacts from a study of 10,000 alleles and include guidelines for interpretation.     

Forensic DNA laboratory automation – Principles and guidelines

There is a lack of clear guidelines for project managers, laboratory managers and forensic scientists on strategies for the automation of forensic DNA laboratory processes and operational implementation of new technologies. This is reflected in the failure rate of projects in the forensic DNA testing environment. We present a set of guidelines and concepts important for forensic laboratory automation. Some case studies from past projects are presented. These consist of partial (or modular) automation (n = 2) and full automated robotically integrated systems (n = 2).Technology Management principles and concepts are crucial to prevent failure of projects, e.g. early adoption of untried technologies, and organizational factors. The future of laboratory automation is modular until such time as new discontinuous technologies will replace the need of the traditional manual laboratory configuration in totality.     

Forensic oral imaging quality of hand-held dental X-ray devices: Comparison of two image receptors and two devices

Recently, different portable hand-held and battery-powered dental X-ray units have become available. Especially for forensic odontological purposes, they offer diverse advantages such as for use in disaster areas and crime-scene locations as also in autopsy rooms and mortuaries. For any application, the most important feature of these hand-held devices is the delivered image quality. The aim of this study is to evaluate the radiographic image quality acquired by two portable X-ray devices in combination with two types of image receptors and to compare the findings with the image quality of a standard intra-oral X-ray device.Eleven samples consisting of eight teeth, two dry skeletal specimens and one formalin-fixed mandible part were mounted on blocks for standardised (re)positioning. Radiological images were acquired with two hand-held (AnyRay^® 60 kVp, 0.02–4.00 mAs and NOMAD^® 60 kVp, 0.023–2.277 mAs) and one wall-mounted (MinRay^® 60/70 kVp 0.14–22.4 mAs) X-ray device combined with two image receptor systems (VistaScan^® phosphor storage plate (PSP) and SIGMA^® M CMOS Active Pixel technology sensor). The effect of X-ray source-to-object distance (SOD) was checked at 20 cm in conjunction with object to image receptor distances (OIDs) of 0.8 and 2.5 cm. For each parameter setup, the exposure times were run from low till high. An expert consent statement was achieved by agreement of four expert observers selecting the optimal images based on a developed four point quality rating system. Next, a selection of the images was assembled in a set of 198 observation screens and scored by seven observers. The observation screens were designed to compare observer scores, relations between devices, receptors and OIDs and images obtained from the different devices at equal exposure levels (mAs). All results were statistically analysed.Radiological image quality was significantly higher for phosphor plate compared with the CMOS digital receptor system (p < 0.0001). Furthermore, a significantly superior image quality was obtained for OID = 0.8 than for OID = 2.5 (p = 0.039). A significant difference in image quality between the three devices was also established (p = 0.02). The present study demonstrated the feasibility of portable X-ray systems for forensic odontological applications based on rendering optimal image quality, provided an in vitro guideline of optimal parameter settings and offered a radiological image database usable in further research.     

Developmental validation studies on the RapidHIT™ Human DNA Identification System

The RapidHIT™ Human DNA Identification System is a fully integrated system (sample in, result out) capable of rapidly generating STR DNA profiles in around 90 min. Here we present a portion of the results from the developmental validation studies performed on the RapidHIT System.     

Evaluation of the composition of street cocaine seized in two regions of Brazil

This work evaluates cocaine purity and the concentration ranges of adulterants and inorganic constituents for 31 street cocaine samples seized in two different regions of Brazil from July 2008 to May 2010. Cocaine and adulterants, such as caffeine, lidocaine and benzocaine, were quantified by Gas chromatography–mass spectrometry (GC–MS), and the inorganic constituents were determined by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) and ion chromatography (IC). The cocaine concentrations in the samples seized in the Amazonas state (AM samples) ranged from 154 to 978 mg g^? 1, and these samples did not contain any of the adulterants studied. The cocaine concentrations in the samples seized in the Minas Gerais state (MG samples) ranged from 63.9 to 753 mg g^? 1. Caffeine was the main adulterant found in 76% of the MG samples, ranging in concentration from 5.5 to 645.3 mg g^? 1. Lidocaine was found in 66.7% of the MG samples, with concentrations ranging from 16.3 to 576.7 mg g^? 1. Benzocaine was found in only one MG sample, at a concentration of 84.8 mg g^? 1. Fourteen elements were identified by ICP-OES, and a wide variation was observed in the concentrations of Ca, Mg, Na, P, Al, Fe, Mn and Zn. Pearson Product–moment Correlations between the analytes allowed the constituents to be associated with the chemicals used in the manufacturing of cocaine and with some common diluents. The study of the purity of cocaine and the presence and concentration of adulterants and inorganic constituents is important because the latter can have deleterious effects on health.     

Multiple murder and criminal careers: A latent class analysis of multiple homicide offenders

PurposeTo construct an empirically rigorous typology of multiple homicide offenders (MHOs).MethodThe current study conducted latent class analysis of the official records of 160 MHOs sampled from eight states to evaluate their criminal careers.ResultsA 3-class solution best fit the data (?2LL = ?1123.61, Bayesian Information Criterion (BIC) = 2648.15, df = 81, L² = 1179.77). Class 1 (n = 64, class assignment probability = .999) was the low-offending group marked by little criminal record and delayed arrest onset. Class 2 (n = 51, class assignment probability = .957) was the severe group that represents the most violent and habitual criminals. Class 3 (n = 45, class assignment probability = .959) was the moderate group whose offending careers were similar to Class 2.ConclusionA sustained criminal career with involvement in versatile forms of crime was observed for two of three classes of MHOs. Linkages to extant typologies and recommendations for additional research that incorporates clinical constructs are proffered.     

SNP genotyping of forensic casework samples using the 52 SNPforID markers

The analysis of degraded DNA is one of the biggest challenges in forensic casework. SNPs, which can be amplified using small amplicons, have previously been successfully applied to the profiling of forensic evidence that could not be analyzed using conventional STRs. Here we selected the 52 SNPforID SNP markers, with amplicons that ranged in size from 59 bp to 115 bp, and used them to profile a range of casework samples from Malaysia. DNA degradation is a common problem in Malaysia due to the high temperatures and humidity. To carry out the study we modified the 52 SNPforID markers into four 13-plex SNaPshot assays to enable easier interpretation of profiles on the ABI PRISM^® 310 and 3500.Fifty-one crime samples comprising bloodstains on cloth, swabs, and a mat and 2 swabs of trace DNA from 10 crime scenes in Malaysia were profiled after DNA extraction using a phenol–chloroform method. The samples were also subjected to STR analysis using the Powerplex^® 16 system (Promega), which resulted in only 17 full profiles and 9 partial profiles; using SNPs, 36 full profiles and 5 partial profiles could be generated.     

Advantage of ForensiX Swabs in Retrieving and Preserving Biological Fluids

This study compares two novel swabs (forensiX) with a standard cotton swab (EUROTUBE) for the collection of saliva stains on glass slide for STR analysis. ForensiX collection tubes are a standard cotton swab in an “active drying” tube, where swab sample is soon dried by its innovative tube surface of the wall. The other is forensiX Nylon Flocked Swab. The study is two phases: The first “phase” assesses swab types regarding to retrieve ability of saliva. The second “phase” compares the drying ability of each swab to assess how crime samples would fare when left in storage. The main result showed that “active drying” is effective to store swabbed sample. The forensiX swabs generally are effective for higher (twofold to fourfold) DNA yield compared to delta lab swab (around 750 pg and 250 pg from 0.5 μL of saliva), respectively. These findings demonstrate the importance of drying performance in the preservation of DNA and swab selection.     

Experimental forensic studies of the preservation of pollen in vehicle fires

The implications of the recent recommendations of the Law Commission regarding the use of admissibility tests have the potential to be far reaching for forensic disciplines that rely on the expertise of highly qualified expert witnesses. These disciplines will need a concomitant body of peer-reviewed experiments that provides a basis for the interpretations of such evidence presented in court. This paper therefore, presents such results from two experiments which were undertaken to address specific issues that were raised in cases presented in the British courtroom. These studies demonstrate that there is a variability in the persistence of Lily, Daffodil and Tulip pollen when exposed to high temperatures between 0.5 min and 1440 min (24 h). It was possible to identify all three pollen types after 30 min of exposure to 400 °C, and after shorter time frames the threshold for successful identification was 700 °C after 0.5 min for all pollen types tested and 500 °C for Daffodil and Lily after 5 min of heat exposure. Over longer time periods (18 h (1080 min)) the different pollen types were found to persist in a viable form for identification at 300 °C (Lily), 200 °C (Daffodil) and 50 °C (Tulip). These findings, albeit from a small sample of pollen types, provide empirical contextual information that would contribute to such evidence having sufficient scientific weight to meet admissibility criteria and be viable evidence for a court. These studies demonstrate the value in seeking pollen evidence from even such extreme crime scenes as encountered in vehicular fires.     

Age estimation by pulp/tooth area ratio in canines: Cameriere's method assessed in an Indian sample using radiovisiography

Age estimation of an individual whether living or dead is an intimidating task in forensic investigations. Since teeth are more resistant to most peri- and post-mortem changes, they are frequently used for identification and age estimation when skeletal remains are in poor condition. However, most methods are destructive and warrant extraction of teeth which is not feasible in living individuals. Cameriere's et al. put forth a radiographic method of age estimation by pulp to tooth area ratio (AR) in canines and revealed a linear regression between age and the AR. In the present study, we estimated the AR in 456 canines (upper, lower and both) in an Indian sample (114 males and 114 females) using radiovisiography technique. Linear regression equations were derived for upper canine, lower canine and both using the AR to estimate chronological age. Additionally, the efficacy of these equations was also evaluated in younger age group (<45 years). The formulas derived, i.e., age = 96.795 ? 513.561x₁ (Eq. (1)) for upper canine, age = 88.308 ? 458.137x₂ (Eq. (2)) for lower canine and age = 99.190 ? 283.537x₁ ? 306.902x₂ + 400.873x₁x₂ (Eq. (3)) for both the canines were applied to predict the chronological age. The mean value of residuals using these regression equations ranged from 4.28 to 6.39 years with upper canine equation generally giving a precise result. When these equations were applied for younger ages (<45 years), the regression equation derived from both canines gave a better result (mean residual 2.70 years). Overall these equations were better able to predict the age in younger ages, i.e., up to 45 years.     

Comparison of the three age estimation methods: Which is more reliable for Turkish children?

BackgroundThree atlases—the GÖK, the Greulich–Pyle (GP), and the Tanner–Whitehouse (TW3)—are used frequently for age determination in Turkey. The purpose of this study was to evaluate the applicability of these three methods related to the skeletal age assessment for Turkish adolescents.Materials and methodsThe conventional roentgenograms of the left hands and wrists, elbows, shoulders, and pelvises of 333 healthy Caucasian children (164 females, 169 males) who fit the study and the criteria of each atlas were obtained. The mean differences (± standard deviation [S.D.] in years) between the chronologic age (CA) and the skeletal age (BA), which were obtained by using each age estimation method, were calculated and tested using t-test.ResultsFor girls, the most accurate method was the TW3 (mean differences (d): ?0.21 (p < 0.05)), following by the GP (d: 0.66 (p < 0.001), and the GÖK (d: 2.99 (p < 0.001)). For boys, the most accurate method was the GP (d: ?0.02 (p > 0.05)), followed by the TW3 (d: ?0.18 (p < 0.05)) and GÖK (d: 1.05 (p < 0.001)).Discussion and conclusionsResults show that the TW3 (for girls) and the GP (for boys) methods are more appropriate than the GÖK atlas for estimating the BA. GÖK could be used for boys aged 11–14 years but it should not be used for girls.     

Collection and direct amplification methods using the GlobalFiler™ kit for DNA recovered from common pipe bomb substrates

When analyzing DNA from exploded pipe bombs, quantities are often in trace amounts, making DNA typing extremely difficult. Amplifying minute amounts of DNA can cause stochastic effects resulting in partial or uninterpretable profiles. Therefore, the initial DNA collection from “touch” evidence must be optimized to maximize the amount of DNA available for analysis.This proof-of-concept study evaluated two different swab types with two direct amplification strategies to identify the most effective method for recovering DNA from common pipe bomb substrates. PVC and steel pipes, electrical tape, and copper wire spiked with epithelial cells were swabbed with cotton or microFLOQ® Direct Swabs and amplified directly or via a pre-treatment prior to STR amplification.Not only was the microFLOQ® Direct Swab protocol the quickest method with the least risk of contamination, but in combination with direct amplification, the microFLOQ® Direct Swabs also generated the most complete STR profiles.     

Detection of acute fentanyl exposure in fresh and decomposed skeletal tissues part II: The effect of dose–death interval

The effects of dose–death interval on the detection of acute fentanyl exposure in fresh and decomposed skeletal tissues (marrow and bone), by automated enzyme-linked immunosorbent assay (ELISA) are described. Rats (n = 14) were administered fentanyl acutely at a dose of 0 (n = 2) or 60 μg/kg (n = 12) by intraperitoneal injection, and euthanized within 20, 45, 135, or 225 min. Femora and tibiae were extracted from the fresh corpses and marrow was isolated from the femoral and tibial medullary cavities. The remains were then allowed to decompose outdoors to the point of complete skeletonization, and vertebrae, pelvi and miscellaneous (humeri and scapulae) were recovered for analysis. In all cases, bones were cleaned in alkaline solution and then ground into a fine powder. Marrow was homogenized in alkaline solution. Fentanyl was extracted from ground bone by methanolic extraction. Extracts were adjusted to pH 6 and analyzed by ELISA. Perimortem heart blood was also collected and diluted in phosphate buffer prior to screening by ELISA. The effect of tissue type on ELISA response was examined through determination of binary classification test sensitivity and the relative decrease in absorbance (%DA, drug-positive tissues vs. drug-free controls) in each tissue type. Overall, the %DA varied significantly between extracts from different skeletal tissues at a given dose–death interval, according to the general order of marrow > decomposed bone > fresh bone. Binary classification test sensitivity values for fentanyl in marrow, fresh epiphyseal (femoral and tibial) bone, fresh diaphyseal (femoral and tibial) bone, decomposed vertebrae, decomposed pelvic bone, and decomposed miscellaneous bone were 67–100%, 0–33%, 0–33%, 0–67%, 0–67% and 0–33%, respectively, over all dose–death intervals. Although group mean %DA values showed a strong negative correlation with dose–death interval in marrow, fresh epiphyseal bone, decomposed vertebrae, pelvic and miscellaneous bone (r = ?0.989, ?0.930, ?0.955, ?0.903, and ?0.974, respectively), the high variability in both fresh and decomposed bone precluded differentiation of the dose–death intervals based on %DA value alone. Overall, the results suggested that the type of skeletal tissue sampled may not be as important as the amount of residual marrow remaining in skeletonized remains.     

Transfer of fibres on the hands of living subjects and their persistence during hand washing

Textile fibres were transferred to the hands of ten living subjects and their persistence was determined after hand washing. Average number of fibres transferred was 300 ± 133 (female 288 ± 92, male 311 ± 163) per 100 cm² hand area in the 100 experiments. However the number of fibres transferred was not gender dependent but individual dependent. The hand texture of subjects was compared with the number of fibres transferred but the relationship was not observed. The number of fibres transferred varied significantly for the 10 repeated experiments performed under the same conditions for the same subject.The subjects were then asked to wash their hands with water. One test group washed their hands with standing water, and the other with running tap water. Afterwards, the number of fibres remaining on the test subjects' hands were investigated. Migration of the fibres on the surface of the observed hands did occur but total loss of transferred fibre after hand washing did not occur. The average number of fibres remaining per 100 cm² hand area was 14 ± 10 (range = 3–72) for hand washing with standing water, and 10 ± 12 (range = 0–79) for washing with running tap water. The results of this study show the possibility of finding fibres on the hands of a person involved in a criminal case even after hand washing before fibre collection.     

Determination of amphetamine-type stimulants,ketamine and metabolites in fingernails by gas chromatography–mass spectrometry

A gas chromatography–mass spectrometry (GC–MS) method was developed and validated for the simultaneous qualification and quantification of methamphetamine (MA), amphetamine (AP), 3,4-methylenedioxy-N-methylamphetamine (MDMA), 3,4-methylenedioxy-N-amphetamine (MDA), ketamine (KET) and norketamine (NKT) in fingernails. Fingernail samples (20 mg) were washed with distilled water and methanol, digested with 1.0 M sodium hydroxide at 95 °C for 30 min, and then extracted with ethyl acetate. Extract solutions were evaporated to dryness, derivatized using heptafluorobutyric anhydride (HFBA) at 60 °C for 30 min, and analyzed by GC–MS. The linear ranges were 0.1–20.0 ng/mg for AP, MDMA and NKT, 0.2–20.0 ng/mg for MA and MDA, and 0.4–20.0 ng/mg for KET, with the coefficients of determination (r² ≥ 0.9989). The intra- and inter-day precisions were within 7.1% and 10.6%, respectively. The intra- and inter-day accuracies were ?10.9% to 0.8% and ?4.3% to 4.5%, respectively. The limits of detections (LODs) and the limits of quantifications (LOQs) for each analyte were lower than 0.094 ng/mg and 0.314 ng/mg, respectively. The recoveries were in the range of 72.3–94.9%. The average fingernail growth rates of two subjects for three years and six subjects for two months were 3.12 mm/month and 3.16 mm/month, respectively. The method proved to be suitable also for the simultaneous detection and quantification of MA, MDMA, KET and their metabolites in fingernails.     

Detection of dermcidin for sweat identification by real-time RT-PCR and ELISA

We evaluated the performance of real-time RT-PCR and ELISA assays for detection of dermcidin (DCD) in sweat and body-fluid stains. DCD, a small antibiotic peptide secreted into human sweat, was detected by real-time RT-PCR in 7-day-old stains containing as small as 10 μL of sweat, and the assay showed high specificity when testing 7-day-old stains containing 30 μL of other body-fluid. ELISA using anti-human dermcidin mouse monoclonal antibody detected DCD sweat diluted up to approximately 10,000-fold and could specifically detect DCD in 10 μL of body-fluid stains. The performance of the two assays was tested during winter on samples that simulated forensic case samples: an undershirt and a sock worn for 20 h, a handkerchief used to wipe the brow several times within 12 h, a cap and a cotton glove worn for 4 h, and a white robe worn at intervals for 2 years. The result showed that the former assay detected DCD in all sites of the undershirt examined (armpit, back, and breast), and the latter gave a relatively high OD value in the armpit among the three sites. For the socks, although the latter assay gave very high OD values in both the center and toe of the foot sole, the former could not detect DCD in both of them. These results indicate that highly damp conditions, such as inside a shoe, might promote the degradation of mRNA in samples such as socks. In the other case samples, sweat was adequately detected by both assays.This study is the first demonstration of the use of real-time RT-PCR to sensitively identify sweat among body-fluid stains, and it confirmed that dermcidin was an excellent marker for sweat identification. In addition, the usefulness of ELISA was also verified. Positive sweat identification using these assays is expected to assist forensic practice.     

The age estimation of blood stains up to 30 days old using visible wavelength hyperspectral image analysis and linear discriminant analysis

A novel application of visible wavelength hyperspectral image analysis has been applied to determine the age of blood stains up to 30 days old. Reflectance spectra from selected locations within the hyperspectral image, obtained from a portable instrument, were subjected to spectral pre-processing. This was followed by the application of a linear discriminant classification model, making estimations possible with an average error of ± 0.27 days for the first 7 days and an overall average error of ± 1.17 days up to 30 days. This is also the first reported study of the determination of the age of fresh blood stains (less than one day old) with an error of ± 0.09 h. The studies have been made under controlled conditions and represent, at this stage, proof of concept results but also are the most accurate age estimation results for measurements between 0 and 30 days reported to date. The results are consistent with well-established kinetic processes suggesting that the pre-processing stages described are revealing spectroscopic changes which are reliably following the time dependent oxidation of HbO₂. The potential for parameterisation of environmental factors to make the method generally applicable at crime scenes is discussed, along with the developments required to further improve classification and to make the instrument genuinely portable.