Stoney David A, Neumann Cedric, Stoney Paul L
Stoney Forensic, Inc., 14101-G Willard Road, Chantilly, VA 20151-2934, USA.
Two N's Forensics, Inc., Brookings, SD 57006-4649, USA; South Dakota State University, Department of Mathematics and Statistics, Brookings, SD 57007, USA.
Forensic Sci Int. 2018 Aug;289:92-107. doi: 10.1016/j.forsciint.2018.05.024. Epub 2018 May 22.
This project used established analytical tools and statistical methods to determine the evidential value of very small particle (VSP) profiles found on handguns, cell phones, drug packaging, and ski masks. Sampling protocols were designed, tested and used to sample VSP from evidence items from a single county-level crime laboratory: 30 handguns, 31 cell phones, 36 drug packaging specimens and 32 ski masks. Specimens were prepared for analysis employing established protocols for semi-automated scanning electron microscopy with elemental characterization by energy dispersive x-ray analysis (SEM/EDS). Statistical methods of particle combination analysis were applied to (1) remove particle "noise" from the datasets, (2) define a set of highly discriminating target particle types, (3) measure the strength of correspondence between profiles, and (4) measure the potential of VSP as an evidence type under defined experimental conditions. Most (84%) of the VSP specimens recovered from common evidence items showed sufficient variety and complexity in their VSP profiles to allow meaningful classification among closed sets of approximately 30 specimens. Correct associations were achieved for 93.5% of test specimens (drug packaging: 97.2%; cell phones: 92.6%; handguns: 92.9%; ski masks 88.2%). Test specimens with VSP numbers greater than 125 showed predominantly correct classifications. These findings establish (1) that VSP are present on the surfaces common items of physical evidence, (2) that the VSP can be efficiently recovered, prepared and analyzed by computer-assisted SEM/EDS analysis, (3) that the variety of particles is sufficient for the definition of classifiers based on reference sources, and (4) that the classifiers perform very well for these particle sets, showing that VSP recovery, analytical methods and computational methods are working effectively. The use of adhering VSP to establish quantitative associations among items of physical evidence is a new approach, exploiting a form of trace evidence that is typically ignored. It is highly significant for its potential to expand the number of cases to which trace evidence can meaningfully contribute and for its ability to include a quantitative statistical approach to data interpretation.
本项目使用既定的分析工具和统计方法来确定在手枪、手机、毒品包装和滑雪面罩上发现的极小微粒（VSP）轮廓的证据价值。设计、测试并使用了采样方案，从一个县级犯罪实验室的物证中采集VSP样本：30把手枪、31部手机、36个毒品包装样本和32个滑雪面罩。采用既定的半自动扫描电子显微镜结合能量色散X射线分析进行元素表征的方案（SEM/EDS）制备样本用于分析。应用颗粒组合分析的统计方法来（1）从数据集中去除颗粒“噪声”，（2）定义一组具有高度区分性的目标颗粒类型，（3）测量轮廓之间的对应强度，以及（4）在规定的实验条件下测量VSP作为一种证据类型的潜力。从常见物证中回收的大多数（84%）VSP样本在其VSP轮廓中显示出足够的多样性和复杂性，以便在大约30个样本的封闭集合中进行有意义的分类。93.5%的测试样本实现了正确关联（毒品包装：97.2%；手机：92.6%；手枪：92.9%；滑雪面罩：88.2%）。VSP数量大于125的测试样本主要显示出正确的分类。这些发现表明（1）VSP存在于常见物证表面，（2）VSP可以通过计算机辅助SEM/EDS分析有效地回收、制备和分析，（3）颗粒种类足以根据参考来源定义分类器，（4）这些分类器对这些颗粒集表现良好，表明VSP回收、分析方法和计算方法正在有效发挥作用。利用附着的VSP在物证项目之间建立定量关联是一种新方法，利用了一种通常被忽视的微量证据形式。它对于扩大微量证据能够有意义地发挥作用的案件数量的潜力以及采用定量统计方法进行数据解释的能力具有重要意义。
