Comparative performance of the Phadebas® Forensic Press Test at room temperature and 37 °C for the detection of saliva stains on fabric exhibits

The Phadebas® Forensic Press Test (PFPT) is an enzyme-based colorimetric test used to visualise and locate latent saliva stains on forensic exhibits. The test relies upon the presence of the enzyme α-amylase which is present in high levels in saliva. Even though the optimal in vitro temperature for α-amylase activity is 37 °C, the PFPT manufacturer’s protocol specifies that the PFPT should be carried out at room temperature (RT). In this study, we compared the performance of the PFPT at RT and 37 °C using combinations of four fabric types (cotton, polyester, acrylic and a cotton/polyester blend), three saliva dilutions (neat, 1:10 and 1:100) and stains aged for four time periods (1 day, 1 week, 1 month and 3 months). The intensity of the PFPT colour reactions at RT and 37 °C were not statistically different across all fabric types, saliva concentrations and stain ages, indicating that maximum sensitivity and performance of the PFPT can be achieved at RT.     

Time-related changes in cardiac ct images of rabbits died from four kinds of execution

Objective To explore the feasibility and appropriate parameters for estimating postmortem interval (PMI) through time-related CT imaging into dynamically monitoring the cardiac changes of rabbits died from four kinds of execution. Methods The experimental rabbits were executed with four disposals of air embolism, strangulation, drowning and hemorrhagic shock. The dead rabbits were observed of their hearts with CT scanning every 6 hours within 120h from the death moment, having the obtained time-different CT images and mean CT values examined. With the cardiac average CT values of rabbits died from discrepant execution, four relevant regression equations were established against the elapsing time (i.e. PMI). Results The CT images of post-death cardiac tissue of rabbits died from one of four executions did change regularly with the PMI elongating, showing consistent with the autopsy verification. The binomial regressive equations were established between the post-death cardiac average CT value and PMI from four executions, demonstrating statistically significant (P<0.05). Conclusion The postmortem cardiac CT imaging into PMI analysis, plus the relating regression equation, provides a new objective visual quantitative approach and reference for forensic medicine to infer the time of death. © 2021, Editorial Office of Forensic Science and Technology. All rights reserved.     

Application of LC−QTOF/MS for the validation and determination of organic explosive residues on Ionscan® swabs

The identification and confirmation of trace explosive residues along with potential precursors and degradation products require a comprehensive laboratory analysis procedure. This study presents the determination of organic explosives consisting of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), 2,4,6-trinitrotoluene (TNT), 2,4,6,N-tetranitro-N-methylaniline (Tetryl), 1,3,5-trinitrobenzene (1,3,5-TNB) and pentaerythritol tetranitrate (PETN) by a high-resolution liquid chromatography quadrupole time-of-flight mass spectrometry (LC−QTOF/MS). The qualitative information including retention time, collision energy, precursor ions, and characteristic fragmentation pattern of each explosive were collected using an atmospheric pressure chemical ionization (APCI) in negative ion mode. The separation efficiency among five compounds was greatly achieved in this study. Four real explosive samples consisting of TNT, RDX, PETN and Tetryl and 12 Ionscan® quality control swabs from the Royal Thai Army were also tested to validate and verify the viability of the GC–MS method used to validate results from an Ionscan® system. The results showed that LC−QTOF/MS is a powerful technique for the identification and confirmation of thermally unstable organic explosives on Ionscan® swabs compared to a conventional GC−MS technique.     

Inter-observer error for area of origin analysis using FARO Zone 3D

In a bloodletting incident, the area of origin (AO) of an impact bloodstain pattern is crucial when establishing the sequence of events. The use of laser scanners and other three-dimensional (3D) technologies to document and analyse bloodstains have been the subject of previous papers, especially where AO analysis is concerned. FARO Zone 3D (FZ3D) is a relatively new software programme that can be used for bloodstain AO analysis. FZ3D requires a greater understanding of inter-observer errors associated with AO. This study looked at the inter-observer variation between 21 examiners when repeatedly calculating the AO six times for a single impact pattern on a plain white wall. An impact rig which consisted of a spring tension arm was positioned and fixed 45 cm from the X wall (right wall), and 45 cm from the Y wall (left wall). This experimental design resembles an impact blow for a bloodletting event. The AO was unknown to all examiners, making it a blind study. The collected results were documented in a Microsoft Excel datasheet and later analysed. From previous literature, a 30 cm acceptable allowance was utilised for AO analysis; however, there is currently no accepted standard error for this type of analysis. The overall total 3D mean error for all examiners was 5.62 cm. The maximum error for any one impact analysis was 24.27 cm. The variation of the data, which was collected by all examiners, was documented as X = 1.14 cm, Y = 1.24 cm, Z = 1.68 cm, and the total 3D error = 2.28 cm. The total 3D error for any one examiner and the variance between examiners did not exceed the 30 cm acceptable allowance utilised in previous literature.     

Preliminary efficiency evaluation of development methods applied to aged sebaceous latent fingermarks

Latent fingermarks are important trace evidence found in crime scenes mainly used for identification purposes. Once deposited, the composition of samples changes over time influencing the efficacy of latent fingermark development methods. In this sense, the aims of this work were to characterize the fatty acid (FA) profile of sebaceous latent fingermarks by GC–FID and to preliminarily evaluate the development efficiency of enhancement methods (powder dusting, iodine fuming and silver nitrate method) in a 30-day period of aging under controlled parameters of temperature, photoperiod and humidity. Results showed that myristic (7.51 ± 0.76% − 13.39 ± 1.26%), palmitic (35.91 ± 1.07% − 40.81 ± 2.52%), stearic (6.67 ± 0.36% − 9.13 ± 0.36%) and oleic (18.08 ± 0.25% − 20.93 ± 0.26%) acid varied significantly (p < 0.05) over the 30-day period of analysis. Regarding development efficiency, fluorescent orange powder and the silver nitrate method also increased their efficacy to develop latent fingermarks over time while the iodine fuming method decreased its efficiency. Silver black powder had constant efficacy in the tested period. Changes in the constitution of sebaceous marks possibly influenced the development efficiency of enhancement techniques. This knowledge is important to better understand the kinetic of aging and its influence on the development method.     

Reliability of a two-dimensional sock-clad footprint linear measurement method

A two-dimensional linear measurement approach for footprints, herein referred to as the “Reel Method,” has been shown to be valid and reliable when used on bare footprints, however, few measurement approaches have been examined on sock-clad footprints. The present investigation examines the validity and reliability of the Reel Method as a two-dimensional linear measurement approach for use on sock-clad footprints.A walking, mid-gait footprint was collected from 30 volunteer participants using the Identicator Inkless Shoe Print Model LE 25P system. The width of the ball of the foot, calcaneal width, and distance from the most posterior aspect of the heel to the most distal aspect of the first toe were each measured and compared between and within three raters. The statistical analysis demonstrated high reliability of the Reel Method among these three raters. The data were found to be normally distributed, and measurements were consistent between and within raters. 95% Intraclass Correlation coefficients, 95% Bland-Altman Limits of Agreement and 95% Standard Error of Measurement determined high statistical agreement between and within raters, demonstrating that the Reel Method is reliable and thus valid for the linear measurement of sock-clad footprints.     

On the discrimination between facial creams of different brands using Raman Spectroscopy and partial least squares discriminant analysis for forensic application

Determining the origin of cosmetic traces is an important aspect of forensic investigations, that helps linking a suspect to a crime. Such type of evidence can help further narrow down the undergoing investigations. This paper reports the first use of Raman Spectroscopy (RS) coupled with the exploratory principal component analysis (PCA) and supervised partial least squares-discriminant analysis (PLS-DA) in facial creams. 40 facial cream samples of 8 different brands were studied in this work. Preliminary assessments through visual inspection of their Raman spectra revealed the presence of oxides, titanium dioxide, castor seed oil, and beeswax. Also, the peaks of alkyne groups were indicative of the presence of talc or mica compounds. The exploratory PCA correctly segregated the samples into 8 clusters and the supervised PLS-DA model correctly classified them into 8 classes. Further evaluation of the performance of the trained PLS-DA model resulted in perfect classification shown by the receiver operating characteristic (ROC) curves. The PLS-DA model also resulted in 100% accuracy of correctly assigning the brand on the face wipes on each of the five substrates viz. cotton, dry and wet tissue paper, nylon substrate, and polyester. This validation was done treating these samples as unknowns. The study has a potential for use under actual forensic casework conditions.     

Performance of forensic facial comparison by morphological analysis across optimal and suboptimal CCTV settings

Facial comparison is an important yet understudied discipline in forensics. The recommended method for facial comparison in a forensic setting involves morphological analysis (MA) with the use of a facial feature list. The performance of this approach has not been tested across various closed-circuit television (CCTV) conditions. This is of particular concern as video and image data available to law enforcement is often varied and of subpar conditions. The present study aimed at testing MA across two types of CCTV data, representing ideal and less than ideal settings, also assessing which particular shortcomings arose from less-than-ideal settings. The study was conducted on a subset of the Wits Face Database arranged in a total of 225 face pools. Each face pool consisted of a target image obtained from either a high-definition digital CCTV camera or a low-definition analogue CCTV camera in monochrome, contrasted to 10 possible matches. The face pools were analysed and scored using MA and confusion matrices were used to analyse the outcomes. A notably high chance corrected accuracy (CCA) (97.3%) and reliability (0.969) was identified across the digital CCTV sample, while in the analogue CCTV sample MA appeared to underperform both in accuracy (CCA: 33.1%) and reliability (0.529). The majority of the errors in scoring resulted in false negatives in the analogue sample (75.2%), while across both CCTV conditions false positives were low (digital: 0.3%; analogue: 1.2%). Even though hit rates appeared deceptively high in the analogue sample, the various measures of performance used and particularly the chance corrected accuracy highlighted its shortfalls. Overall, CCTV recording quality appears closely associated to MA performance, despite the favourable error rates when using the Facial Identification Scientific Working Group feature list.     

刑事技术在毒品走私案侦办中的重要作用

毒品走私案件的侦办是一个不断思考和发现的过程。以刑事技术为指导的侦查理论思维更具科学性、系统性和实践性,是一种侦办毒品走私案科学化和现代化的思维方式,对于侦办复杂多变的毒品走私案件具有重要作用。