Forensic applications of hyperspectral imaging technique: a narrative review

Hyperspectral imaging (HSI) collects and processes information from the entire electromagnetic spectrum to obtain the spectrum of each pixel in the image of a scene, with the aim of finding objects and identifying materials. It is a non-contact, non-destructive technology that can be used without modifying or altering the analysed target. Forensic analysis and crime scene investigations are two of the most investigated fields of application, being able to detect and analyse many types of evidence.In this paper we analysed the most commonly reported forensic science applications.The literature indicates that the fields in which HSI appears most promising are the analysis of blood traces, document forgery, gunshot residues and the identification of fingerprints.

Correction of Substrate Spectral Distortion in Hyper-Spectral Imaging by Neural Network for Blood Stain Characterization

In the recent past, hyper-spectral imaging has found widespread application in forensic science, performing both geometric characterization of biological traces and trace classification by exploiting their spectral emission. Methods proposed in the literature for blood stain analysis have been shown to be effectively limited to collaborative surfaces. This proves to be restrictive in real-case scenarios. The problem of the substrate material and color is then still an open issue for blood stain analysis. This paper presents a novel method for blood spectra correction when contaminated by the influence of the substrate, exploiting a neural network-based approach. Blood stains hyper-spectral images deposited on 12 different substrates for 12 days at regular intervals were acquired via a hyper-spectral camera. The data collected were used to train and test the developed neural network model. Starting from the spectra of a blood stain deposited in a generic substrate, the algorithm at first recognizes whether it is blood or not, then allows to obtain the spectra that the same blood stain, at the same time, would have on a reference white substrate with a mean absolute percentage error of 1.11%. Uncertainty analysis has also been performed by comparing the ground truth reflectance spectra with the predicted ones by the neural model.

[The analysis of the results of the medical criminalistics expertises of the blood stains performed at the Bureau of Forensic Medical Expertise of the Moscow Health Department during the period from 2011 till 2015]

The objective of the present study was the analysis of the results of the medical criminalistics expertises of the blood stains with reference to their different characteristics including the occurrence across the years, variability, the forms and parameters of the traumatizing impacts, the properties of the objects with which the injuries were inflicted, etc. The majority of the data necessary for the analysis were extracted from the archive materials of the Medical and Criminalistic Department of the Bureau of Forensic Medical Expertise of the Moscow Health Department for the period from 2011 till 2015. A total of 5749 expertises performed during this time included 107 analyses of blood stains, 98 trace-evidence and 9 situational analyses. The specific features of such expertises include a large number of objects carrying blood stains available for the analysis. In the majority of the cases, such objects are stained with blood of several types differing in the mechanisms of their formation. 3D-scanning of the scene of the event with the subsequent three-dimensional computer-assisted simulation of the actions of each participant of the accident is considered to be the most promising method for the medical criminalistic expertise of the blood stains. The application of this approach is believed to make the work of the forensic medical experts significantly easier.

[The specific features of the blood stains depending on their volume]

The objective of the present study was to determine the minimal and maximum volume of blood droplets freely falling from various droplet-forming surfaces and to characterize the specific morphological features of the resulting stains. The experiments were designed so that the blood droplets were allowed to fall down from the height of 10 cm to 1.5 m. The drop volume varied from 5 mcl to 134 mcl depending on the shape of the objects and the area of the droplet-forming surfaces. The size of the blood stains ranged from 0.4 to 2.4 cm. The stains of a smaller size were regarded as splashes while a stain resulting from the fall of a droplet having a volume greater than 200 mcl was considered to be a result of merging of several droplets and was termed 'blood volume'. The morphological features of the blood stains of different volume are described.

[Effect of Benzidine Test on DNA Analysis of Bloodstain]

OBJECTIVES

To explore the effect of benzidine test and related reagents on DNA analysis of bloodstain.

METHODS

A total of 970 bloodstain filter paper samples with 1 μL venous blood were collected, and 10 of them acted as control samples. After benzidine test and related reagent processing, DNA of 960 samples was extracted by Chelex-100 and silica bead methods and then multiplex amplified by AmpFℓSTR™ Identifiler™ Plus PCR kits. The results of STR typing were compared between different groups.

RESULTS

DNA were extracted immediately after benzidine test. Totally STR loci （3.80±1.34） were detected by silica bead method, while no STR loci were obtained by Chelex-100 method. Thirteen samples （21.7%） with whole STR typing results were obtained by drying after benzidine test, and the STR locus number （12.90±1.49） which obtained by silica bead method was much higher than by Chelex-100 method （4.70±1.96） （P<0.05）. When DNA was extracted immediately after the addition of glacial acetic acid, the STR locus number was （9.40±2.09） by silica bead method, but no STR typing result was obtained by Chelex-100 method. All 15 STR loci could be obtained by only adding glacial acetic acid after drying and only adding tetramethylbenzidine alcoholization liquid or 3% hydrogen peroxide liquid.

CONCLUSIONS

Benzidine test has significant influence on DNA analysis of bloodstain. The Chelex-100 method is not suitable for the DNA extraction of bloodstain after benzidine test. Drying after benzidine test and silica bead methods can effectively enhance the STR locus number of bloodstain.

[The peculiar morphological features of the blood stains on the snow over of different density]

The objective of the present study was to elucidate the peculiar morphological features of the blood stains on the snow over of different density. We have undertaken the modeling and investigation of the blood stains on the loose snow cover (ρ=0.35±0.03 g/cm³) and at the areas of snow compacted by a motor-vehicle wheel (ρ=0.96±0.03 g/cm³) with the use of the visual, metric, descriptive, and statistical methods. The analysis of the blood stain patterns on the loose snow showed that a blood drop tends to form a depressed cylindrical canal at the bottom of which an irregularly shaped spherical element can be seen; it is composed of small snow crystals soaked with blood. The upper end of the canal has the fine-scalloped edge tending to shed unevenly. The morphological picture of the blood stains at the compacted snow cover is similar to that on the hard wettable rough surfaces; they have the oval shape and the unevenly serrated edge with the well apparent signs of sputtering.at the periphery.

[The peculiar morphological features of the imprints of straight and wavy head hair dirtied with blood]

The objective of the present study was to elucidate the specific morphological features of the imprints of blood-soaked straight and wavy head hair. The contact imprints of straight and wavy head hair dirtied with blood were obtained experimentally. The imprints of straight hair were shown to exhibit the elements in the form of the rectilinear and bow-shaped slightly bent stripes. The imprints of wavy hair were shaped as the arches, waves, circles, and a large number of various small elements, such as dashes and commas.

[The specific features of the blood stains on the water-lubricated surfaces]

The objective of the present study was the experimental investigation of the morphological characteristics of the 20 mcl blood droplets which freely fell down onto the surfaces that were either dry or moderately and profusely lubricated with water. The morphological properties of the resulting blood stains on the glass surfaces, dry or moderately and profusely lubricated with water, are described. The most characteristic features of such stains at the wet surface were the uneven serrated and stripe-like prominences, radial 'lucent stripes' passing into the splashing elements. The size of the blood stains at the water-lubricated surface increased by 8-44%.

Infrared imaging of the crime scene: possibilities and pitfalls

All objects radiate infrared energy invisible to the human eye, which can be imaged by infrared cameras, visualizing differences in temperature and/or emissivity of objects. Infrared imaging is an emerging technique for forensic investigators. The rapid, nondestructive, and noncontact features of infrared imaging indicate its suitability for many forensic applications, ranging from the estimation of time of death to the detection of blood stains on dark backgrounds. This paper provides an overview of the principles and instrumentation involved in infrared imaging. Difficulties concerning the image interpretation due to different radiation sources and different emissivity values within a scene are addressed. Finally, reported forensic applications are reviewed and supported by practical illustrations. When introduced in forensic casework, infrared imaging can help investigators to detect, to visualize, and to identify useful evidence nondestructively.