Estimation of the age of human bloodstains is of great importance in forensic practices, but it is a challenging task because of the lack of a well-accepted, reliable, and established method. Here, the attenuated total reflection (ATR)-Fourier transform infrared (FTIR) technique combined with advanced chemometric methods was utilized to determine the age of indoor and outdoor bloodstains up to 107 days. The bloodstain storage conditions mimicked crime scene scenarios as closely as possible. Two partial least squares regression models—indoor and outdoor models with 7–85 days—exhibited good performance for external validation, with low values of predictive root mean squared error (5.83 and 4.77) and high R2 values (0.94 and 0.96) and residual predictive deviation (4.08 and 5.14), respectively. Two partial least squares–discriminant analysis classification models were built and demonstrated excellent distinction between fresh (age ≤1 d) and older (age >1 d) bloodstains, which is highly valuable for forensic investigations. These findings demonstrate that ATR-FTIR spectroscopy coupled with advanced chemometric methods can be employed as a rapid and non-destructive tool for age estimation of bloodstains in real-world forensic investigation.

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The short tandem repeat (STR) loci used in human genetic studies are characterized by having relatively high mutation rates. In particular, to ensure an appropriate evaluation of genetic evidence in parentage and forensic analyses, it is essential to have accurate estimates of the mutation rates associated with the commonly used autosomal and sex chromosome STR loci. Differences in STR mutation rates between different ethnic groups should also be determined. Mutation data from two laboratories working with different ethnic groups were extracted from many meiotic transmissions ascertained for 15 autosomal STR loci currently used in forensic routine. Forty-five thousand and eighty-five trios were checked for the biological consistency of maternity and paternity through the analysis of a minimum of 15 loci. Mutations were scored as paternal, maternal, or ambiguous according to the most parsimonious explanation for the inconsistency, using always the least requiring hypothesis in terms of number of repeat differences. The main findings are: (a) the overall mutation rate across the 15 loci was 9.78 × 10(-4) per gamete per generation (95% CI = 9.30 × 10(-4)-1.03 × 10(-3)), and with just 48 (out of 1,587) exceptions, all of the mutations were single-step; (b) repeat gains were more frequent than losses; (c) longer alleles were found to be more mutable; and (d) the mutation rates differ at some loci between the two ethnic groups. Large worldwide meiotic transmission datasets are still needed to measure allele-specific mutation rates at the STR loci consensually used in forensic genetics.

Massively parallel sequencing (MPS) has rapidly become a promising method for forensic DNA typing, due to its ability to detect a large number of markers and samples simultaneously in a single reaction, and sequence information can be obtained directly. In the present study, two kinds of forensic genetic markers, short tandem repeat (STR) and identity-informative single nucleotide polymorphism (iiSNP) were analyzed simultaneously using ForenSeq DNA Signature Prep Kit, a commercially available kit on MPS platform. A total of 152 DNA markers, including 27 autosomal STR (A-STR) loci, 24 Y chromosomal STR (Y-STR) loci, 7 X chromosomal STR (X-STR) loci and 94 iiSNP loci were genotyped for 107 Tibetan individuals (53 males and 54 females). Compared with length-based STR typing methods, 112 more A-STR alleles, 41 more Y-STR alleles, and 24 more X-STR alleles were observed at 17 A-STRs, 9 Y-STRs, and 5 X-STRs using sequence-based approaches. Thirty-nine novel sequence variations were observed at 20 STR loci. When the flanking regions were also analyzed in addition to target SNPs at the 94 iiSNPs, 38 more alleles were identified. Our study provided an adequate genotype and frequencies data of the two types of genetic markers for forensic practice. Moreover, we also proved that this panel is highly polymorphic and informative in Tibetan population, and should be efficient in forensic kinship testing and personal identification cases. Several genetic markers have been introduced to forensic genetics to clarify the problems of kinship analysis and personal identification. Short tandem repeats (STRs) and single nucleotide polymorphisms (SNPs) are commonly used genetic markers in present forensic cases 1,2. STRs, usually 2-6 bp in length, are commonly typed with the amplified fragment length polymorphism (Amp-FLP) strategy combining fluorescently labelled multiplex PCR and capillary electrophoresis (CE) 3. Allele calling can thus be inferred from fragment length by comparison with a locus specific allelic ladder that has been previously sequenced, where the number of repeat units is distinct 2. Thus, each allele is regarded as a lengthbased (LB) allele using this approach. With the advancement of sequencing technologies over the last decade, the existence of sequence structure variations in alleles with the same length has been uncovered 4. SNPs, which could be amplified with smaller amplicons, are bi-allelic genetic markers with lower mutation rates compared with STRs 5. Several autosomal SNP marker sets and detection methods, such as single-base extension, chip-based microarrays, and allele-specific hybridization arrays, have been developed to compensate for the relatively weaker discrimination power of single loci caused by the bi-allelic nature of the human genome 5-7. However, these methods are not widely used in forensic practice due to the requirement of higher DNA inputs or the limited ability to detect a vast number of SNP loci in a single reaction 8. Different from detection methods mentioned above, massively paralle...

The determination of time since death or the postmortem interval (PMI) is one of the most important and frequently asked questions in forensic medicine. Medicolegal scholars and forensic pathologists around the world have studied the estimation of PMI extensively in the past, and many novel methods and advanced technologies have now been applied in the field. For several centuries, Chinese forensic examiners have also worked on the estimation of the PMI, and there are a large number of excellent studies published in Chinese rather than in English, and these are not easily accessible or known internationally. Therefore we have conducted a review of relevant studies published by Chinese forensic scholars in the last few decades. The scope of this review is to provide a concise summary of the current progress in the estimation of PMI by Chinese forensic researchers using molecular biology, spectroscopic technology, entomological methods, energy changes, thanatochemistry and other methods.

Estimating PMI is of great importance in forensic investigations. Although many methods are used to estimate the PMI, a few investigations focus on the postmortem redistribution. In this study, ultraviolet–visible (UV–Vis) measurement combined with visual inspection indicated a regular diffusion of hemoglobin into plasma after death showing the redistribution of postmortem components in blood. Thereafter, attenuated total reflection–Fourier transform infrared (ATR–FTIR) spectroscopy was used to confirm the variations caused by this phenomenon. First, full-spectrum partial least-squares (PLS) and genetic algorithm combined with PLS (GA-PLS) models were constructed to predict the PMI. The performance of GA-PLS model was better than that of full-spectrum PLS model based on its root mean square error (RMSE) of cross-validation of 3.46 h (R2 = 0.95) and the RMSE of prediction of 3.46 h (R2 = 0.94). The investigation on the similarity of spectra between blood plasma and formed elements also supported the role of redistribution of components in spectral changes in postmortem plasma. These results demonstrated that ATR-FTIR spectroscopy coupled with the advanced mathematical methods could serve as a convenient and reliable tool to study the redistribution of postmortem components and estimate the PMI.

Postmortem interval (PMI) determination is one of the most challenging tasks in forensic medicine due to a lack of accurate and reliable methods. It is especially difficult for late PMI determination. Although many attempts with various types of body fluids based on chemical methods have been made to solve this problem, few investigations are focused on blood samples. In this study, we employed an attenuated total reflection (ATR)-Fourier transform infrared (FTIR) technique coupled with principle component analysis (PCA) to monitor biochemical changes in rabbit plasma with increasing PMI. Partial least square (PLS) model was used based on the spectral data for PMI prediction in an independent sample set. Our results revealed that postmortem chemical changes in compositions of the plasma were time-dependent, and various components including proteins, lipids and nucleic acids contributed to the discrimination of the samples at different time points. A satisfactory prediction within 48h postmortem was performed by the combined PLS model with a good fitting between actual and predicted PMI of 0.984 and with an error of ±1.92h. In consideration of the simplicity and portability of ATR-FTIR, our preliminary study provides an experimental and theoretical basis for application of this technique in forensic practice.