1种“新型”粉尘痕迹固定剂——发胶

在诸多刑事案件现场中,罪犯遗留下的立体、平面痕迹较多,这类痕迹大多用拍照方法进行提取,如果直接用石膏粉灌注,很容易使特征尤其是细节特征遭到破坏。公安部第二研究所研制的HH-固定剂,无疑解决了这方面的难题。但这种固定剂价格高,且不易买到。实践中,我们试用市场流行的发胶(固定发型用),对粉尘立体、平面痕迹进行固定,再用石膏粉灌注提取。痕迹的特征反映清晰、完整、稳定,并可长期保存,效果和价格均优于HH-固定剂,显示出了极大的优越性。     

环形闪光灯在现场勘查中的运用

环形闪光灯具有脱影功能，用于尸体解剖照相效果极佳。用于检验照相时，通过光比控制、多次控制等方法，可以更好地显现物证的细节及立体层次感。将环形闪光灯作为垂直同轴光、暗视场照明的光源，可以清晰提取微弱痕迹、手印。[编者按]     

球形表面手印胶带纸提取方法

如何提取球面客体表面已通过粉末方法显现的手印痕迹,是痕迹检验工作的一项重要研究内容。笔者经多次摸索实验表明,只要改进胶带纸的粘取方法,就可以有效地提高球面客体表面手印的提取效果,提取到完整或相对完整的手印痕迹。     

刑侦石膏制模快速提取法

传统的石膏制模法固化速度较慢,影响犯罪痕迹的提取。为了适应打击犯罪的需要,经多年摸索,笔者研制成功“刑侦石膏制模快速提取法”,使传统的石膏制模固化时间缩短了一半,且各种性能不低于以前的制模方法,并扩大了证据提取的范围。     

失效石膏提取立体足迹失败后的补救

1993年1月3日,某车站发生一起车盗案件,在路基下的蚕豆地里发现犯罪分子留下的立体足迹。因经验不足,误用受潮的工业石膏灌注制模,结果3天后仍未凝固,呈粘糊状,无法提取。后在该蚕豆地里进行实验,用医用石膏进行补救取得了成功,下面简要介绍提取的方法: (1)用一把小汤匙,把足迹上呈粘糊状的石膏轻轻地取出,取时一定要小心谨慎,不要破坏底层的痕迹,约取出三分之二即可; (2)在痕迹表面均匀地洒上一层医用石膏粉;     

“相纸转印YH染料擦显法”的正确利用和改进

在现场勘查时，最多见的就是灰尘加层或减层痕迹。对于灰尘痕迹一般采取的提取方法有照相法、透明胶带贴取法、静电吸附法、背胶纸贴取法和相纸转印法等技术。上述几种灰尘痕迹提取方法当中，前4种方法操作简单，但是对灰尘痕迹的灰尘量要求较多，提取后的反差小。相纸转印法虽然操作程序比较复杂，转印贴取技术要求较高，但是对痕迹的灰尘量要求不多，显现后痕迹细节特征反映非常好，排除背景干扰。     

宁夏南部地带现场立体指纹石膏制模提取方法

近几年，随着农村耕畜价格的不断上涨，在宁夏南部农村，案犯采用攀爬越墙、挖洞人室等手段盗窃农机、耕畜的案件不断增加，在现场除留有工具、足迹等常见痕迹外，往往在现场出入口墙面及攀爬辅助物一一土坎上留有立体指纹。由于受散光及其它条件地限制，技术员很难用拍照等常规方法提取。     

景深混合在痕迹检验中的应用

本文以三维视频显微镜观察采集多幅景深不同的弹壳底部痕迹图片,通过使用Photoshop软件中进行景深混合操作为例,将多幅相同视野大小、相同曝光参数、景深不同的痕迹图像,通过软件进行景深混合得到更大景深、更大清晰范围的痕迹图像,有利于提高枪弹痕迹检验工作质量。同时抛砖引玉,该方法可用于数码相机还有利用体式显微镜、立体显微镜等光学仪器的影像检验。     

变压器中硒钢片上油渍指印的拍照方法

在现场勘查中常常遇到一些必须用拍照方法才能提取的加减层指掌印痕迹。对于其中与客体有反差的指印痕迹,可直接加接圈或延长皮腔,使镜头与痕迹中心成一直线拍照成原物大方法进行提取即可。但有的客体上的指掌印痕迹垂直观察是看不到痕迹的,垂直拍照也就更不行了。如变压器中绝缘油浸泡后触摸的硒钢片上的加减层指印痕迹,油渍指印痕迹与黑红色硒钢片溶成一色,正面观察无任何反差,拍照后看不清痕迹,只是黑板一块。可通过半逆光侧面观察,硒钢片上油渍反光呈白色,指印乳突线所遗留的凹痕又呈黑色,用延     

浅谈现场灰尘痕迹的提取

在提取现场灰尘痕迹时可直接拍照，未曾见过有关其他提取方法的报道，而现场灰尘痕迹有的直接拍摄反差微弱无法检验，有的受所处位置、角度等条件的限制，无法直接拍照。在实践中，笔者摸索出一种较为简便有效的方法。既可以加强灰尘痕迹的反差，消除灰尘痕迹背景表面的图案干扰，又能直接提取拍摄，使现场灰尘痕迹的提取利用率有了极大的提高，介绍如下。１适用范围１．１平面上的灰尘加减层手印、足迹应以平滑坚实的平面上的灰尘加减层手印、足迹为主。而且平面承受客体上的灰尘均匀细薄。比如平面上的灰尘减层指印，平面承受客体被细薄灰…     

The recovery of latent fingermarks and DNA using a silicone-based casting material

There are many techniques available for the recovery of fingermarks at scenes of crime including the possibility of taking casts of the marks. Casts can be advantageous in cases where other destructive recovery techniques might not be suitable, such as when recovering finger marks deposited on valued or immobile items. In this research, Isomark (a silicone-based casting material) was used to recover casts of finger marks placed on a variety of substrates. Casts were enhanced using cyanoacrylate fuming. Good quality marks were successfully recovered from a range of smooth, non-porous surfaces. Recovery from semi-porous surfaces was shown to be inefficient. DNA was subsequently extracted from the casts using QIAamp Mini extraction kits, amplified and profiled. Full DNA profiles were obtained 34% of samples extracted.     

Individualizing characteristics of footprints in Gujjars of North India--forensic aspects

Careful examination of foot impressions can provide important evidences and clues in a crime scene investigation. The present study is conducted on a cross-sectional sample of 1040 adult male Gujjars inhabiting the sub-Himalayan region of North India. The study describes the utility of individualizing characteristics of footprints in forensic examinations. Various features of the toes, humps in the toe line, phalange marks, flatfoot condition, pits, cracks, corns, etc., were studied. Frequency of some of these characters has also been recorded. The frequency of the tibialis-type foot is the highest, followed by fibularis-type, then intermediate-type and midularis-type is found to be least frequent among the sample. Three humps have been found most often in footprints, followed by two humps, four humps, and then five humps and one hump are found to be least frequent. Flatfoot condition is found to be present in 1.54% of the sample population and the trait also shows bilateral variation. Phalange marks, crease marks, pits, deformity, etc., are also demonstrated with suitable examples in the present population. These characteristic features can provide useful clues to establish personal identity whenever complete or partial footprints are recovered at the crime scene and can help in including or excluding the possible presence of individual at the scene of crime.     

Heat and let dye: Part II – Rapid heat-fixing of blood traces

Blood-contaminated shoeprints and footmarks contain valuable operational information as they may bind an individual who stepped in the crime scene with the incident and not merely with the location. As determining the age of a bloodstain remains a challenge, while processing the scene, it is difficult to determine whether the blood is completely, or partially, dry. Thus, executing a dye staining protocol may wash these marks away as they might still be soluble. However, to meet this challenge, it is possible to fix blood marks using heat. This study aims to find a solution for floor surfaces covered by heavier blood traces (shoeprints and footmarks). For this purpose, a new pseudo-operating device was constructed for examining the blood-fixing process of both mentioned trace types. Two trials were performed with depletion marks. The results revealed that fully developed fresh and heavily blood deposits were obtained by heating to 200°C for 7.5 min using the fixing device, followed by a staining protocol using amido black solution. The achieved sharp resolution of the examined bloody prints demonstrates that in certain cases the dehydration mechanism of heating is preferred over precipitating the proteins attributed to 5-sulfosalycilic acid; thus, reducing the risk of washing blood evidence while processing the crime scene.     

Classification of firing pin impressions using HOG-SVM

Crimes, such as robbery and murder, often involve firearms. In order to assist with the investigation into the crime, firearm examiners are asked to determine whether cartridge cases found at a crime scene had been fired from a suspect's firearm. This examination is based on a comparison of the marks left on the surfaces of cartridge cases. Firing pin impressions can be one of the most commonly used of these marks. In this study, a total of nine Ruger model 10/22 semiautomatic rifles were used. Fifty cartridges were fired from each rifle. The cartridge cases were collected, and each firing pin impression was then cast and photographed using a comparison microscope. In this paper, we will describe how one may use a computer vision algorithm, the Histogram of Orientated Gradient (HOG), and a machine learning method, Support Vector Machines (SVMs), to classify images of firing pin impressions. Our method achieved a reasonably high accuracy at 93%. This can be used to associate a firearm with a cartridge case recovered from a scene. We also compared our method with other feature extraction algorithms. The comparison results showed that the HOG-SVM method had the highest performance in this classification task.     

Chemical enhancement of footwear impressions in blood deposited on fabric — Evaluating the use of alginate casting materials followed by chemical enhancement

Most footwear marks made in blood on a surface such as fabric tend to be enhanced in situ rather than physically recovered using a lifting technique prior to enhancement. This work reports on the use of an alginate material to recover the impressed footwear marks made in blood and deposited on a range of fabric types and colours. The lifted marks were then enhanced using acid black 1 and leuco crystal violet with excellent results.This presents a new method for the lifting and recovery of blood impressions in situ from crime scene followed by subsequent mark enhancement of the lifted impression.     

Comparison of Dimensional Accuracies Using Two Elastomeric Impression Materials in Casting Three‐dimensional Tool Marks

The purpose of this study was to evaluate two types of impression materials which were frequently used for casting three‐dimensional tool marks in China, namely (i) dental impression material and (ii) special elastomeric impression material for tool mark casting. The two different elastomeric impression materials were compared under equal conditions. The parameters measured were dimensional accuracies, the number of air bubbles, the ease of use, and the sharpness and quality of the individual characteristics present on casts. The results showed that dental impression material had the advantage of special elastomeric impression material in casting tool marks in crime scenes; hence, it combined ease of use, dimensional accuracy, sharpness and high quality.     

Bolt Cutter Blade's Imprint in Toolmarks Examination

Bolt cutters are known as cutting tools which are used for cutting hard objects and materials, such as padlocks and bars. Bolt cutter blades leave their imprint on the cut objects. When receiving a cut object from a crime scene, forensic toolmarks examiners can determine whether the suspected cutting tool was used in a specific crime or not based on class characteristic marks and individual marks that the bolt cutter blades leave on the cut object. The paper presents preliminary results of a study on ten bolt cutters and suggests a quick preliminary examination—the comparison between the blade thickness and the width of the imprint left by the tool on the cut object. Based on the comparison result, if there is not a match, the examiner can eliminate the feasibility of the use of the suspected cutting tool in a specific crime. This examination simplifies and accelerates the comparison procedure.     

The Effect of Image Alterations on Identification Using Palmar Flexion Creases

Palmprints are identified using matching of minutia points, which can be time consuming for fingerprint experts and in database searches. This article analyzes the operational characteristics of a palmar flexion crease (PFC) identification software tool, using a dataset of 10 replicates of 100 palms, where the user can label and match palmar line features. Results show that 100 palmprint images modified 10 times each using rotation, translation, and additive noise, mimicking some of the characteristics found in crime scene palmar marks, can be identified with a 99.2% genuine acceptance rate and 0% false acceptance rate when labeled within 3.5 mm of the PFC. Partial palmprint images can also be identified using the same method to filter the dataset prior to traditional matching, while maintaining an effective genuine acceptance rate. The work shows that identification using PFCs can improve palmprint identification through integration with existing systems, and through dedicated palmprint identification applications.     

Improve Toolmarks' Impressions in Soft Wax

When the forensic toolmarks laboratory receives for examination and comparison a tool that is suspected of having been involved in a crime, the expert performs tests designed to determine whether or not the specific tool generates the same toolmarks as those found at the crime scene. This is performed by testing tool striation on a piece of soft metal, such as lead, and examining the marks left by the tool. Studies have shown that wax may be an optimal material for this purpose. This study examines the use of wax at different temperatures and shows that quality of results is better when the wax is cooled (recommended temperature is ?18°C). At this temperature, the wax is flexible enough but does not smear and is not sticky. This makes the obtained marks clearer and of better quality.     

Shoeprint image retrieval and crime scene shoeprint image linking by using convolutional neural network and normalized cross correlation

A shoeprint image retrieval process aims to identify and match images of shoeprints found at crime scenes with shoeprint images from a known reference database. It is a challenging problem in the forensic discipline of footwear analysis because a shoeprint found at the crime scene is often imperfect. Recovered shoeprints may be partial, distorted, left on surfaces that do not mark easily, or perhaps come from shoes that do not transfer marks easily. In this study, we present a shoeprint retrieval method by using a convolutional neural network (CNN) and normalized cross-correlation (NCC). A pre-trained CNN was used to extract features from the pre-processed shoeprint images. We then employed NCC to compute a similarity score based on the extracted image features. We achieved a retrieval accuracy of 82% in our experiments, where a “successful” retrieval means that the ground truth image was returned in the top 1% of returned images. We also extend our shoeprint retrieval method to the problem of linking shoeprints recovered from crime scenes. This new method can provide a linkage between two crime scenes if the two recovered shoeprints originated from the same shoe. This new method achieved a retrieval accuracy of 88.99% in the top 20% of returned images.