物证鉴定范式发展(一):传统明确结论范式

王桂强

刑事技术 ›› 2024, Vol. 49 ›› Issue (4) : 331-339. DOI: 10.16467/j.1008-3650.2024.0028
论著

物证鉴定范式发展(一):传统明确结论范式

作者信息 +

Forensic Paradigm Development. Part 1: The Traditional Paradigm of Categorical Conclusions

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摘要

物证鉴定范式是解释物证结果证据意义并形成鉴定意见过程中采用的科学理论和方法。物证鉴定领域正在经历从传统的物证来源明确结论范式向物证结果似然比评估范式转换。传统物证鉴定范式以特征唯一性作为科学基础假设,已有100余年发展和应用历史,应用于除DNA物证以外的几乎所有物证。鉴定人通过检测和比对物证和样本特征确定二者特征是否匹配,并采用阈值决策方式给出物证和样本来源相同或来源不同意见。基于物证明确来源意见和案件其他证据信息,决策者再做出相关的行为事实推论,作为被告犯罪与否的中间证据事实。在传统范式中,鉴定人从物证和样本特征结果得到物证明确来源意见的过程是一个演绎推理过程:大前提是物证特征唯一性假设,小前提是特征匹配(或不匹配)结果,结论是物证和样本来源相同(或不同)。只要大前提和小前提为真,传统范式的来源明确意见就正确。然而,随着DNA物证结果概率评估方法的发展和成熟,一些学者质疑特征唯一性假设缺少实证证明,进而认为失去这一前提的传统范式的演绎推理无效,因此传统物证来源明确意见范式被认为缺少坚固的科学基础。

Abstract

The forensic paradigm is the scientific theories and methods used in the process of interpreting the findings of forensic examination and forming expert opinion. There is a paradigm shift from the traditional paradigm of categorical source conclusions to the paradigm of evaluative opinion. The traditional forensic paradigm is based on the assumption of feature uniqueness. The traditional paradigm of forensic science has a history of over 100 years of development and application, and has been applied to almost all physical evidence except DNA evidence. After detecting and comparing trace evidence from crime scene and known source sample, examiner will determine whether the features of the trace evidence match features of the sample, and will use threshold decision-making to give opinions on the trace evidence and the sample came from a same source or from different sources. In the traditional paradigm, the process by which examiner forms a categorical source opinions from results of the features is a deductive reasoning process: the major premise is the assumption of the uniqueness of trace features, the minor premise is the results of feature matching (or no-match), and the conclusion is that the trace and sample has same (or different) source. As long as the major and minor premises are true, the categorical opinion on source of the traditional paradigm is correct. However, with the development and maturity of evaluative methods for forensic DNA results, some scholars questioned the lack of empirical proof for the hypothesis of feature uniqueness in the traditional forensic paradigm, and thus believe that deductive reasoning without a major premise of the assumption of the trace features uniqueness has no validity, and therefore, the categorical source opinion in the traditional paradigm lacks a solid scientific foundation.

关键词

物证鉴定 / 特征匹配 / 阈值决策 / 明确结论 / 传统范式

Key words

forensic science / feature matching / threshold decision-making / categorical conclusions / traditional paradigm

引用本文

导出引用
王桂强. 物证鉴定范式发展(一):传统明确结论范式. 刑事技术. 2024, 49(4): 331-339 https://doi.org/10.16467/j.1008-3650.2024.0028
WANG Guiqiang. Forensic Paradigm Development. Part 1: The Traditional Paradigm of Categorical Conclusions. Forensic Science and Technology. 2024, 49(4): 331-339 https://doi.org/10.16467/j.1008-3650.2024.0028
物证鉴定是用科学技术方法检验和解释犯罪现场物证包含的相关信息,以帮助解决法律关注的问题。物证鉴定过程包括提取犯罪现场物证和相关样本、检验物证和样本获得物证结果、解释物证结果证据意义并形成鉴定意见,以及应用鉴定意见等环节。最近30年来,物证鉴定取得了革命性进步,主要体现在两个方面:1)以DNA检测为代表的物证检验技术进步,特别是检测灵敏度的持续提高,显著增加了物证结果的信息含量,同时也增加了物证结果的复杂性;2)解释物证结果证据意义所采用的科学理论和方法的演进,即物证鉴定范式发展,革命性地提升了物证结果解释能力和物证结果意见证据的科学有效性,并在本质上变革了物证鉴定意见证据的推理证明模式。
科学范式是指某一科学领域内公认和共同遵循的理论体系及研究模式[1]。物证鉴定结果解释范式(简称物证鉴定范式),是在物证鉴定中解释物证结果证据意义并形成鉴定意见过程中采用的科学理论和方法。目前,物证鉴定领域正在经历范式转换和范式拓展过程:1)从以指印比对鉴定为代表的传统明确来源结论范式[2],向以DNA比对鉴定为代表的物证特征似然比范式[3-4]的转换;2)从物证特征似然比范式,向以人脸和声音比对为代表的物证分数似然比范式[5-6]的拓展。
物证鉴定范式演进是科学层面上的进步,其重要性甚至超过物证检验技术进步。物证鉴定似然比范式在科学基础假设和结果评估方法,以及鉴定意见的形成、表述、理解和推理应用等方面,完全不同于传统明确结论范式[3-4]。在世界范围,物证似然比范式已经走进刑事司法诉讼。新范式提升了物证鉴定意见的科学有效性和证据价值,但也给物证鉴定和刑事司法诉讼提出了新要求,并带来了巨大挑战。物证鉴定从业人员和司法诉讼各参与方都应该理解和掌握物证鉴定传统范式和似然比范式的科学基础、理论和方法,并跟踪物证鉴定范式最新发展,确保决策者(指使用物证鉴定意见的任何人,如检察官、律师、法官和侦查员等)能够正确理解和适当应用物证鉴定似然比意见。
本文是物证鉴定范式发展系列论文的第一篇,将论述物证鉴定传统明确结论范式的特征检测和比对、鉴定意见形成和表述、鉴定意见的推理应用,以及传统范式的科学基础争议。传统物证鉴定范式经历了100余年的发展和应用,也是物证鉴定范式转换的起点,理解和掌握传统范式物证结果解释的理论和方法具有重要意义。本系列论文的第二篇将论述物证鉴定似然比范式的贝叶斯似然比框架;论文三将论述DNA特征客观似然比范式;论文四将论述形态特征主观似然比范式;论文五将论述人脸相似分数似然比范式;论文六将讨论物证鉴定范式转换现状和面临的挑战,以及未来发展路径。

1 物证来源鉴定与传统明确结论范式

1.1 物证来源鉴定及作用

物证来源鉴定是物证鉴定的核心任务之一[2]。物证来源鉴定的目的是解决或帮助解决法律关注的犯罪现场物证来源问题,即一个未知来源的犯罪现场物证(简称物证)与一个已知来源的样本(简称样本)是否来自同一特定来源,或两个未知来源的犯罪现场物证是否有共同来源。在物证来源鉴定中,鉴定人通过检测和比较物证特征与样本特征的一致性或整体相似性结果,再基于对检验结果的解释给出物证来源鉴定意见,直接回答或帮助回答物证和样本来源是否相同问题。
物证来源鉴定及应用流程如图1所示。首先,检验物证和样本并获取相关属性信息,包括特征信息和整体信息。第二步,比对物证和样本的属性,得到关于物证和样本的特征一致性或总体相似性的物证结果。第三步,解释物证和样本特征一致性或总体相似性结果,即评估物证结果的证据意义,并形成关于物证来源的鉴定意见,包括来源明确意见和来源支持意见。最后,基于鉴定意见和案件其他证据信息,决策者进一步推理得出物证相关的争议事实推论,包括:基于来源明确意见和其他案件证据信息推理确定物证相关的行为事实;基于来源支持意见和其他案件证据信息推理确定物证来源事实,并进一步推理确定物证相关的行为事实。
图1 物证来源鉴定及应用流程

Fig.1 The procedure of forensic source determination and its application

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物证来源鉴定在刑事司法诉讼中发挥着非常重要和关键的作用。基于物证来源鉴定意见得到的来源或行为事实推论,被作为中间证据或次最终项证据,最后与案件所有其他证据结合,将帮助决策者做出嫌疑人是否犯罪的最终证明[7]。物证鉴定意见的科学属性,使基于其形成的中间证据项通常具有更好的可靠性。

1.2 物证结果解释

物证结果解释是评估物证检验结果的证明意义和证据价值。它是物证鉴定的核心环节,也是物证证据价值的增值过程。
在当前刑事司法实践中,物证结果解释范式有两大类:1)传统的以指印鉴定为典型代表的来源明确结论范式[2]。鉴定人基于物证和样本特征的一致性程度是否达到某个阈值,给出物证和样本来源相同或不同的明确结论意见,直接回答了法律关注的犯罪现场物证来源问题[2]。2)以DNA鉴定为典型代表的物证结果似然比范式[3-4]。鉴定人基于在两个对立的来源或行为命题下物证结果出现概率的比值(似然比),给出物证来源或行为支持性鉴定意见,即物证结果对来源相同和来源不同事实主张或一对争议行为事实主张的相对支持意见,帮助决策者确定物证的来源或行为事实[3]

1.3 传统的物证来源明确结论范式

物证来源明确结论范式是指鉴定人通过检验、比对和评估未知来源物证和已知来源样本特征,确定二者特征是否一致,并基于特征的一致性是否达到某个阈值,给出物证和样本来源相同或来源不同的二元明确鉴定意见。物证来源明确结论范式历经100余年的应用和发展,已经建立了完整的理论和方法体系,覆盖了除DNA以外的几乎所有类型物证[2],也被称为特征阈值决策范式,或简称明确结论范式或传统范式。
图2示意了传统范式物证来源鉴定意见形成和应用流程。鉴定人得出物证来源二元明确意见需要经过特征检测、特征比对、特征一致性阈值评估、来源意见形成四个基本步骤。最后,基于物证明确来源鉴定意见,并结合物证相关信息和案件其他证据信息,决策者再做出与物证相关的行为事实推断,进而作为嫌疑人犯罪与否的中间证据。
图2 传统范式物证来源鉴定意见形成和应用流程

Fig.2 The formation and application procedure of forensic opinions on source determination in traditional paradigm

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2 传统范式鉴定意见的形成和类型

2.1 鉴定意见形成过程

传统范式物证来源鉴定意见形成涉及四个基本步骤,见图2
第一步是检测物证和样本特征。鉴定人通过视觉或仪器方法检测物证和样本的来源相关特征,这些特征分为两大类:个体特征和种类特征[2]。个体特征是可以建立物体唯一性的独特特征,如指印的脊线细节特征组;种类特征是一类物体共同具有的、能够与其他类物体区分的共性特征,如鞋印的花纹形态特征,种类特征不能建立唯一性。
第二步是特征比对。鉴定人比对物证和样本特征的一致性,并做出二者特征匹配、不匹配和不确定三种决定[2]。如果不能确定物证和样本特征是否存在足够差异或足够相似,鉴定人将做出不确定特征是否匹配的决定。物证和样本特征存在本质差异(不可解释差异)将导致不匹配决定。如果物证和样本特征是不可区分地相似,且所有存在的差异是可解释的,鉴定人将决定二者特征匹配。
第三步是阈值决策。鉴定人进一步评估特征匹配结果的意义和价值,以确定物证和样本特征匹配的程度(特征数量和质量的组合)是否达到可以给出“来源相同”结论的阈值。阈值是鉴定人做出特定分类决定所需要的特征一致性值,它可以是定量或定性的。
第四步是意见形成。鉴定人基于特征匹配与否的决定和匹配阈值评估结果,做出二元来源意见:1)基于特征不匹配决定,给出物证和样本来源不同的明确意见;2)基于特征不确定决定,给出无结论意见;3)基于匹配特征的阈值评估结果给出来源意见,特征匹配程度低于阈值的将给出无结论意见,特征匹配程度超过阈值将给出物证和样本来源同一的意见。
由于涉及的物证对象和特征属性不同,各物证专业来源鉴定的具体方法可能有所不同,但这些方法都基于相同的步骤、原理和逻辑推理路线。最典型的是指印鉴定采用的ACE-V方法,其中字母ACE分别表示检验、比对和评估,V表示另一鉴定人复核鉴定[8]

2.2 个体和种类同一鉴定意见

传统范式物证来源鉴定意见可以分为两大类[2]:1)个体同一来源意见;2)种类同一来源意见。
基于物证与样本没有本质特征差异并且有足够的个体特征匹配,鉴定人可以得出物证和样本来源自同一个体并完全排除来自其他个体可能性的意见,即个体同一认定结论。如果物证和样本个体特征不一致且差异不可解释,将得出个体同一否定意见。在鉴定实践中,能够给出个体同一认定意见的常见物证有指印、枪弹痕迹、工具痕迹、鞋印、整体分离痕迹、笔迹、声音和人脸等。
基于物证与样本种类特征一致性,鉴定人可以给出二者来源种类同一认定或否定意见。当物证和样本种类特征有足够的一致性且没有不可解释的差异,将给出来源种类同一认定意见。如果物证和样本存在种类特征差异且不可解释,鉴定人将给出来源种类同一否定意见。常见的种类同一认定物证包括玻璃、纤维、油漆、泥土、塑料、花粉等微量物证,以及鞋底和轮胎花纹等形态类物证。

2.3 鉴定意见形成要点

在传统物证鉴定范式中,鉴定人确定物证和样本特征匹配与否和评估匹配特征是否达到阈值的决策过程通常不是简单明了的。首先,鉴定人必须避免混淆个体特征和种类特征。虽然大多数物证专业已经能够详细定义各种特征的种类和个体属性,但部分专业的种类和个体特征分类是含糊的,增加了个体和种类特征混淆的风险。
其次,鉴定人必须正确解释和区分物证和样本特征差异的性质。由于生成条件变化,同一来源物证和样本特征通常也不完全等同,总是存在某种程度的差异。鉴定人需要确定出现的特征差异是不同来源生成的本质性差异(不可解释差异),或是同一来源因生成条件变化导致的非本质差异(可解释差异)。差异解释很大程度依赖鉴定人的专业判断,具有主观性且易受认知偏误影响,因此容易造成鉴定人间的决策差异。
第三,鉴定人做出特征匹配阈值决策需要一个“内心确认”或“信心飞跃”的过程。匹配特征的特异性是由特征数量和质量组合决定的[9]。但是,特征质量一般缺少客观量化指标,鉴定人通常是根据自身训练和经验主观决定特征质量的价值,因此需要通过一个“内心确认”[10]或“信心飞跃”[11]过程确定能否做出个体同一认定意见。

2.4 传统范式的科学逻辑

传统物证鉴定范式经过长期发展,已经形成了成熟的科学理论体系,包括两个基础假设(唯一性假设和持久性假设)[2]和两个原理(洛卡德物质交换原理和柯克个体同一认定原理)[2],以及鉴定意见形成和应用的推理逻辑。它们构成了传统物证鉴定范式的理论框架,覆盖了传统范式物证来源鉴定过程及鉴定意见推理应用所需要的科学基础和理论,为物证明确来源意见证据的有效性提供了科学保障。
物证特征唯一性的哲学基础是自然界中的模式形成在其形态结构上绝不重复[12],或 “自然界从不重复自身”[13]。物证特征唯一性是一个假设,这个假设不能通过实证确认[14],但它在一定程度上得到了生物学、化学和物理学的支持和解释,也得到了实践观察和经验的支持[15]。例如,实证证明指纹特征具有唯一性必须比较世界上所有人的指纹,但这是不可能完成的任务。指纹特征唯一性假设只能被以下两点支持[16]:1)通过长期实证观察证据,目前还没有发现两个人有完全一样的指纹;2)通过脊线皮肤形成理论,支持脊线细节形态生成的随机多样性。
传统范式的个体同一认定意见形成过程逻辑是演绎推理[17-18],它是前提包含结论的有效演绎:前提为真,结论正确。这个推理的大前提是唯一性假设,即每个物品具有其唯一性特征,其延伸公理表述为特征匹配的两个物品只能来自同一来源,特征不匹配的两个物品只能来自不同来源;小前提是特征检验结果,即物证和样本特征匹配(或不匹配)的结果;推理结论是“物证和样本来源相同(或不同)”。这是典型的演绎三段论,只要大前提唯一性假设和小前提特征匹配(或不匹配)结果正确,传统范式来源鉴定意见就有坚固的逻辑基础。

3 传统范式鉴定意见的表述和理解

3.1 鉴定意见表述方式和含义

传统范式物证来源鉴定意见表述相对简单明了,通常包括三种意见:1)物证和样本来源相同(认定意见);2)物证和样本来源不同(否定意见);3)无结论或不确定(不能确定物证和样本来源是否相同)[2]
个体同一认定意见,通常表述为物证和样本来源相同或有共同来源,或物证来自样本供体。例如,指印同一认定意见表述为“犯罪现场指印与样本指印来自同一个手指”,或“犯罪现场指印来自嫌疑人的右手食指”。个体同一认定意见的本质含义是物证和样本是来自同一人或同一物,并且完全排除来自其他人或物体的可能性。个体同一否定意见通常表述为物证和样本来源不同,或物证不是来自样本供体,其本质含义是排除物证来自样本供体。
实践中,一些类型物证(如笔迹鉴定和牙痕鉴定等)可能给出物证来源等级意见(多级梯度意见),如“认定”“倾向认定”“不能确定”“倾向否定”和“否定”五级意见。这种等级来源意见一定程度叙述了物证来源相同或不同结论的确定性程度。
种类同一来源认定意见,通常表述为物证与样本来自相同种类,或某某特征“一致”“相同”或“符合”。例如,纤维种类同一认定意见表述为“犯罪现场纤维与嫌疑人衣服纤维种类相同”,泥土种类同一认定意见表述为“嫌疑人鞋上泥土与犯罪现场泥土样本的元素成分和矿物组成相同”。种类同一认定意见表明物证和样本是来自同一类别的群体,其本质含义是不能排除但也不能确定二者来自同一个体来源。种类同一否定意见通常表述为物证和样本种类不同或来源不同,或用特征“不同”或“不一致”等表达种类否定意见。这类意见的本质含义是物证和样本不是来自同一类人群或物,即二者有不同来源。

3.2 鉴定意见表述原则

清楚准确地表达物证鉴定意见是鉴定人的职责,也是鉴定意见证据的价值基础。传统范式的物证来源鉴定意见表述应该满足以下基本要求。
第一,必须明确陈述来源意见的性质和方向:是个体同一或是种类同一,是同一认定或是否定[2]
第二,应该清楚地陈述同一认定意见的强度,即同一性程度。个体同一认定结论通常明确地叙述了绝对性来源意见。但是,对于种类同一认定意见,由于缺少可靠的种类特征频率或稀有性的定量数据,实践中通常无法给出特征匹配价值的意见。理想状态下,应该陈述匹配特征的频率。如果没有可用的定量频率数据,鉴定人可以基于经验和专业知识定性地叙述特征频率或稀有性,如“这种类型白色纤维很常见”,或“这种玻璃折射率很稀有”,使得决策者可以相对更好地理解种类同一来源意见的意义[2]
第三,必须给出明确的来源意见,不能仅报告特征检测结果或特征匹配结果。如果鉴定人只叙述物证和样本特征检测结果或特征匹配结果,而不做出明确来源意见,势必将让外行的决策者确定检测结果或特征匹配结果的意义,可能导致物证结果的弃用、滥用或误用[19]。例如,没有达到鉴定人决策阈值的特征匹配结果,很可能被决策者误解为物证和样本有共同来源的结论。
第四,应该全面陈述获得来源鉴定意见所依靠的前提事实、知识和假定,包括依据的特征类型、数量和质量,以及特征符合情况等,以便其他专家和决策者根据需要进行评估和质疑。
第五,应透明地报告两名(或多名)鉴定人的分歧意见。当鉴定人员出现意见分歧时,实验室的通常做法是组织产生分歧的专家相互讨论,形成共识意见并只报告共识意见,而不提及最初的意见分歧。在大多数情况下,协商一致意见作为专家共享的共同结论是有价值的,但同时明确报告最初的分歧意见情况对决策者是有帮助的[20]

3.3 鉴定意见传递和理解

总体而言,传统范式物证来源鉴定意见表述通常是直接明确的,其含义的传递和理解也相对简单明了。只要鉴定人规范地表述和传达其鉴定意见,经过适当培训的决策者通常能够相对容易地正确理解二元或等级物证来源意见的含义并适当应用,一般不会出现歧义。但是,不合规的来源鉴定意见(如仅叙述特征或特征匹配结果,或种类同一认定意见没有明确叙述种类认定性质),或决策者在相关物证鉴定知识方面培训不足,也可能引发误解和错误应用。

4 传统范式鉴定意见的推理应用

传统范式物证来源鉴定意见直接回答了法律关注的犯罪现场物证来源问题。但是,物证来源意见仅仅解决了物证是否来自一个特定来源的中间证据事实问题(例如犯罪现场窗户上提取的指印来自嫌疑人手指),并不能直接回答嫌疑人是否存在相关行为事实的次最终项事实问题(例如嫌疑人爬窗户进入犯罪现场室内的行为事实),更没有直接回答嫌疑人是否有罪的最终证明项问题[7]。法律将物理证据归为“间接证据”[2]。间接证据的一个重要特征是它需要一个推理将证据事实(evidentiary fact)与主要事实(principle fact)联系起来[2]。因此,在刑事司法证明中,需要将来源鉴定意见关于物证来源的证据事实转换成关于嫌疑人相关行为的主要事实,进而与其他证据一起成为法庭裁定有罪与否的事实要素。
基于物证鉴定意见做出行为推论需要使用物证TPPR属性信息,TPPR是转移性(transfer)、持久性(persistence)、流行性(prevalence)和检出性(recovery)英文单词的首字母缩写[21]。行为推理还需要物证相关信息(如犯罪现场信息、物证分布信息和物证属性信息等),以及案件其他证据信息(如调查证据信息和其他物证鉴定结论信息)[2]。这是一个归纳推理过程,因此行为推论总是存在不确定性。
在刑事司法实践中,基于物证来源明确意见做出的行为事实推论是法庭裁定依靠的关键证据之一。但是,基于传统范式物证来源鉴定意见做出相关行为推论是相当复杂的任务。首先,嫌疑人接触行为可能不是犯罪现场物证形成的唯一方式,还存在其他可能方式,例如物证物质间接转移(二次或多次转移)和物证污染,甚至是伪造物证。其次,“物证”可能与犯罪活动是不相关的,例如嫌疑人在犯罪活动之前到过现场留下了指印(背景指印)。第三,行为推理依赖物证来源鉴定意见、物证形态和分布信息、物证TPPR属性数据(知识)等各种资料信息,充分收集和应用这些资料信息是很大的挑战。第四,由于影响推论的因素众多并且一般难以量化,决策者评估行为推论的不确定性主要依靠主观判断,增加了决策难度。第五,可获得的相关资料信息的不完整性和资料自身的不确定性,也会导致行为推论存在不确定性[2]
基于物证来源鉴定意见的行为推理是归纳性质的,会导致多种可能的行为推论,包括对被告有利和不利的行为推论。尽管通过尽可能多地组合使用其他证据信息可以提高行为推论的确定性,但推断出百分之百确定的某个特定行为推论通常是不可能的。决策者需要结合案件其他证据信息“排除合理怀疑”地认定相关行为事实。为提高行为推论的确定性以尽可能达到排除合理怀疑的证据标准,可以从多个方面努力。一是通过有效的实验室质量管理提升物证来源鉴定意见的可靠性;二是通过大量实证研究提供更加全面和可靠的相关物证TPPR数据;三是组合使用可获得的其他相关物证鉴定结果和鉴定意见信息;四是尽可能多地收集和综合使用案件的其他证据信息。
需要特别强调的是,基于物证来源鉴定意见推理得出相关行为推论是决策者的责任。鉴定人不应该给出关于行为推论的意见,因为使用案件的其他证据信息做出行为推论显然超越了鉴定人的职责范围。只有决策者可以合法地组合使用物证来源鉴定意见、物证TPPR数据和案件的其他证据信息,并排除合理怀疑地做出事实推论。但是,相对通常是技术外行的决策者,鉴定人员在掌握、理解和应用对行为推理非常重要的物证TPPR数据方面具有明显优势。因此,鉴定人可以主动提供和更新相关物证TPPR数据或知识信息,帮助决策者做出更有信息依据的行为推论。

5 传统范式受到质疑和批评

随着DNA物证鉴定和应用的兴起,DNA特征结果似然比方法被认为是物证结果解释的金标准[4,21]。在这个金标准参照下,传统范式物证来源鉴定意见的科学性受到质疑。科学家们开始质疑传统范式的核心假设,即唯一性假设[22-23]。一些政府和行业组织的报告也批评传统范式的唯一性主张[20,24-27]
批评者从多个方面质疑传统鉴定范式的科学基 础[28]。首先,强烈质疑“唯一性”这一基础假设,认为这个假设迄今没有被证实并且也无法被证实[14,18,29-33],因此唯一性假设是不科学和形而上学的[15]。有批评者认为,物证特征唯一性必须被限定为一种教条(信条),因为它是建立在归纳推理的基础上,是从特定的陈述(基于观察或经验)到普遍规律或理论的推理路线,这个来自归纳推理的特征唯一性结论不一定是正确的[18]。没有唯一性假设,传统范式形成个体同一认定结论的演绎推理就没有了真实的大前提,导致个体同一认定结论缺少合理的逻辑基础。其次,批评者提出,即使存在哲学上的物体“唯一性”,物证鉴定实践中检验的有限特征组的唯一性也没有实证基础。第三,鉴定人给出个体同一认定来源结论被认为是篡夺了决策者的任务[13,29-30,33]。第四,即使唯一性假设成立,鉴定人也可能无法可靠地辨别和解释物证特征,因而不能可靠地应用个体同一认定科学得出可靠的明确来源结论[14,31]。第五,个体同一认定方法的“信心飞跃”理论是不科学的[14,34]。第六,没有唯一性假设,想要基于物证与样本特征匹配结果演绎推理得到个体同一认定结论,就需要排除物证的潜在来源群体中所有其他个体的可能性。对于开放的潜在来源群体(如“地球人口群体”),这种排除是不可能完成的,因此物证个体同一认定的推理过程不可能是演绎的,只能是归纳的[35]
物证鉴定领域内的专家学者对上述批评和质疑有不同反应。许多专家支持或同意这些批评和质疑[34],另一些专家坚持“唯一性”假设[36]或为传统鉴定范式辩护[37-39]
面对质疑,传统范式的物证来源鉴定意见表述也做出一些改良。一些物证鉴定行业组织在行业规范或标准中弱化了传统范式来源鉴定意见表述的绝对性[40]。然而,这些改变仍然坚持了明确同一来源意见的性质,在本质上没有变化。另外,一些鉴定机构采用概率评估方法。例如,美国陆军刑事调查实验室(United States Army Criminal Investigation Laboratory,USACIL)在2015年宣布放弃“个体同一认定”一词,并在贝叶斯概率框架内报告其结果[41]。2017年,USACIL进一步宣布实施统计软件应用程序FRStat,为指纹鉴定提供概率评估支持[42]。此外,美国法庭科学领域委员会组织(Organization of Scientific Area Committees,OSAC)发布了指印脊线检验结论标准[43],以似然比格式重新定义术语“认定”,向概率表达方式迈出了一步。

6 传统范式的特点和发展

传统范式物证来源鉴定意见具有若干优势。一是其鉴定意见直接、明确地回答了法律关注的物证来源问题,特别是个体同一认定意见的来源唯一性属性与法律事实调查追求的唯一性目标高度一致。二是其鉴定意见表述相对简单明了,外行人员易正确理解意见的含义。
传统范式物证来源鉴定意见也存在若干弱点。第一,比对鉴定过程存在较大主观性(特别是形态特征比对鉴定)。在特征确定、特征匹配决策和匹配特征阈值决策环节,鉴定人主要是基于自身的培训和经验做出的主观判断。鉴定人依赖主观判断有多种原因:1)一些物证特征本身缺少明确定义或难以明确定义;2)缺乏特征匹配的明确决策标准;3)普遍缺乏特征匹配价值评估标准(没有相关的特征频率数据)。虽然鉴定人的主观性并不一定等同于鉴定意见的不可靠性,但主观性在一定条件下可能带来一些负面效果,包括容易出现人为错误,更容易受到认知偏误影响,鉴定人之间更容易表现不一致等。相比之下,客观、量化的方法往往会达到更高的准确性、可重复性和可靠性。第二,一些传统物证来源鉴定方法有效性评价普遍不足,包括没有经过严格的方法确认程序审查,或方法确认结论没有公开发表接受同行评审,或缺乏明确的方法适用范围和方法错误率数据等。第三,物证种类同一认定意见通常没有表达同一强度信息,如纤维、玻璃、泥土等物证。实践中,这类鉴定意见一般用特征“一致”“符合”“可以形成”或“不排除”等词语表述种类同一认定意见,而无法有效传达物证检验结果的证据强度,可能导致鉴定意见被弃用、误用或滥用。
虽然一些学者和从业者强烈质疑传统物证鉴定范式的科学基础,并呼吁实施“范式转移”(从传统明确来源结论范式转换到物证结果似然比范式),但在刑事司法实践中,目前传统范式物证鉴定意见在全球范围仍然被普遍接受和采用。
为了适应现代科学和社会发展水平的新要求,传统物证鉴定范式也需要进一步发展和改进。第一,开展基础研究工作,持续强化传统物证来源鉴定结论的科学基础。唯一性假设是传统物证鉴定范式的基石。如前所述,对物证鉴定的唯一性假设进行完全实证验证是不可能的,但可以采用波普尔“实证可证伪性标准”作为物证唯一性假设的验证标准[16,18]。物证鉴定领域应该系统性地开展“证伪研究”,验证各类物证特征“唯一性”假设的“逼真度”是否达到满足实际应用要求的确证程度,为传统范式物证明确来源意见的有效性提供更坚固的科学基础。
第二,对各类物证鉴定方法开展严格方法确认,确保物证来源鉴定方法的科学有效性[44]。在案件应用之前,必须通过实证研究证明传统物证来源鉴定方法的有效性,包括基础有效性、应用有效性,并明确方法的适用范围、局限性和错误率等。
第三,在物证鉴定实验室质量管理体系中强化认知偏误管理。现有的研究表明,认知偏误可以显著影响物证鉴定意见形成并可能导致错误结论[45-47]。实验室可以采用适当程序和方法有效管理物证鉴定信息以减少认知偏误错误,包括依次序透露和线性依次序透露方法、样本或现场物证队列方法、盲平行鉴定和盲评审、案件主管分离方法和案件背景信息管理系统等[48-49]
第四,通过实证研究,改进和拓展传统范式物证来源明确意见表述方式,减少决策者错误理解和应用鉴定意见的风险。
第五,开展基于物证来源明确意见推断和确定行为事实的方法和理论研究,开发行为推理模型,提升物证相关行为推论的确定性和证据价值。

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摘要
在法庭科学中,特征比对是进行物证检验的核心方法之一,应用于几乎所有专业。基于统计框架的特征比对客观方法,是当前法庭科学发展的方向。本文就影像专业的人脸特征比对方法展开研究。通过深入分析当前基于深度学习的人脸特征进行比对的特点,开展了大规模数据的特征比对实验,统计了深度学习特征比对分数的分布,结合贝叶斯统计框架下基于分数似然比的模型,提出基于深度学习特征相似度分数似然比的人脸比对方法。我们的实验结果和分析,支撑了人脸特征比对客观方法的实际应用,也丰富了基于统计的法庭科学特征比对方法。
(LI Zhihui, XIE Lanchi, WANG Guiqiang, et al. Facial comparison based on likelihood ratio of similarity score obtained from deep-learning into features[J]. Forensic Science and Technology, 2019, 44(1): 1-8.)
Feature-comparison is one of the core methods among forensic evidence test, almost being applied by every professional subject. The feature-comparison method, based on the statistical framework, is objective, thus becoming the on-going direction of forensic science. Facial feature comparison is explored in this paper. Through in-depth characteristic analysis of the current deep learning with face features, the facial feature comparison is carried out into relevant large-scale data, thereby having obtained the statistical distributions of facial feature comparison score by deep-learning. Accordingly, the facial comparison approach is proposed at the basis of features' deep-learning coupled into the model of score-based likelihood ratio under Bayesian framework. The experimental results are supportive for the facial feature comparison to apply, demonstrating one more enrichment of the methods about forensic feature comparison based on statistics.
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The field of forensic science has profited from recent advances in the elicitation of various kinds probabilistic data. These provide the basis for implementing probabilistic inference procedures (e.g., in terms of likelihood ratios) that address the task of discriminating among competing target propositions. There is ongoing discussion, however, whether forensic identification, that is, a conclusion that associates a potential source (such as an individual or object) with a given item of scientific evidence (e.g., a biological stain or a tool mark), can, if ever, be based on purely probabilistic argument. With regard to this issue, the present paper proposes to analyze the process of forensic identification from a decision theoretic point of view. Existing probabilistic inference procedures are used therein as an integral part. The idea underlying the proposed analyses is that inference and decision are connected in the sense that the former is the point of departure for the latter. As such the approach forms a coordinated whole, that is a framework also known in the context as 'full Bayesian (decision) approach'. This study points out that, as a logical extension to purely probabilistic reasoning, a decision theoretic conceptualization of forensic identification allows the content and structure of arguments to be examined from a reasonably distinct perspective and common fallacious interpretations to be avoided.
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The forensic sciences are under review more so than ever before. Such review is necessary and healthy and should be a continuous process. It identifies areas for improvement in quality practices and services. The issues surrounding error, i.e., measurement error, human error, contextual bias, and confirmatory bias, and interpretation are discussed. Infrastructure is already in place to support reliability. However, more definition and clarity of terms and interpretation would facilitate communication and understanding. Material improvement across the disciplines should be sought through national programs in education and training, focused on science, the scientific method, statistics, and ethics. To provide direction for advancing the forensic sciences a list of recommendations ranging from further documentation to new research and validation to education and to accreditation is provided for consideration. The list is a starting point for discussion that could foster further thought and input in developing an overarching strategic plan for enhancing the forensic sciences.
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Recent challenges have brought the discipline of firearms and tool mark identification to the forefront in recent court cases. This article reviews those challenges and offers substantial support for the scientific foundations of the firearms and tool mark identification discipline. A careful review of the available literature has revealed that firearms and tool mark identification is rooted in firm scientific foundations, critically studied according to the precepts of the scientific method culminating in the Association of Firearms and Toolmark Examiners' Theory of Identification. Firearms and tool mark identification has been validated in a manner appropriate for evidence of the kind to be expected in firearms and tool mark examinations. Proficiency tests and error rates have been studied and can provide consumers of the disciple with a useful guide as to the frequency with which misidentifications are reported in the community using appropriate methodologies and controls. As a result, the primary issues in recent challenges do not invalidate the firearms and tool mark discipline as a science nor should it detract it from its admissibility in a court of law.
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(WANG Guiqiang. Method validation and method SOP in forensic science[J]. Forensic Science and Technology, 2006, 31(6): 3-8.)
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COOPER G, METERKO V. Cognitive bias research in forensic science: a systematic review[J]. Forensic Science International, 2019, 297: 35-46.
The extent to which cognitive biases may influence decision-making in forensic science is an important question with implications for training and practice. We conducted a systematic review of the literature on cognitive biases in forensic science disciplines. The initial literature search including electronic searching of three databases (two social science, one science) and manual review of reference lists in identified articles. An initial screening of title and abstract by two independent reviewers followed by full text review resulted in the identification of 29 primary source (research) studies. A critical methodological deficiency, serious enough to make the study too problematic to provide useful evidence, was identified in two of the studies. Most (n = 22) conducted analyses limited to practitioners (n = 17), forensic science trainees (n = 2), or both forensic science practitioners and students (n = 3); other analyses were based on university student or general population participants. Latent fingerprint analysis was examined in 11 studies, with 1-3 other studies found in 13 other disciplines or domains. This set of studies provides a robust database, with evidence of the influence of confirmation bias on analysts conclusions, specifically among the studies with practitioners or trainees presented with case-specific information about the "suspect" or crime scenario (in 9 of 11 studies examining this question), procedures regarding use of exemplar(s) (in 4 of 4 studies), or knowledge of a previous decision (in 4 of 4 studies). The available research supports the idea of susceptibility of forensic science practitioners to various types of confirmation bias and of the potential value of procedures designed to reduce access to unnecessary information and control the order of providing relevant information, use of multiple comparison samples rather than a single suspect exemplar, and replication of results by analysts blinded to previous results.Copyright © 2019 The Authors. Published by Elsevier B.V. All rights reserved.
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In recent years, a number of studies have demonstrated that forensic examiners can be biased by task-irrelevant contextual information. However, concerns relating to methodological flaws and ecological validity attenuate how much the current body of knowledge can be applied to real-life operational settings. The current review takes a narrative approach to synthesizing the literature across forensic science. Further, the review considers three main issues: (i) primary research on contextual bias within forensic science; (ii) methodological criticisms of this research; (iii) an alternative perspective that task-irrelevant contextual information does not always lead to error. One suggestion for future research is outlined, which is that studies on contextual bias in forensic decisions should be conducted in collaboration between forensic scientists and cognitive psychologists. Only then can rigorous and ecological valid experiments be created that will be able to assess how task-irrelevant contextual information influences forensic analysis and judgments in operationally valid settings.© 2019 American Academy of Forensic Sciences.
[47]
王桂强. 物证鉴定错误问题研析[J]. 刑事技术, 2017, 42(6): 431-440.
摘要
物证鉴定错误是物证鉴定结果、结论或意见所表达和反映的事实情况本质上偏离了真实的事实情况,其包括物证鉴定结论错误和结论传递、理解及应用错误。依照错误来源,物证鉴定错误可以分为仪器错误、方法错误、认知偏见错误和人为错误四种类型。依照错误性质,物证鉴定错误可以分为物证来源鉴定结论的假阳性和假阴性错误、物证成分检验结论的定性和定量错误和物证推断检验结果错误。物证鉴定错误发生阶段,涉及物证发现、提取、包装、保存、特征检验、特征解释评估、结论报告和传递、结论理解和应用全过程。虽然现有的物证鉴定准确性和有效性的实证研究资料还无法给出能够反映实际案件物证鉴定情况并被广泛认同的一般错误率值,但这些资料已经表明包括指印、DNA、枪弹、咬痕、笔迹和毛发等常见物证的鉴定结论确实存在一定错误风险,并且这些实证研究资料可以帮助总结研究物证鉴定错误的出现规律和发现物证鉴定体系的薄弱点。
(WANG Guiqiang. Dissection on forensic error[J]. Forensic Science and Technology, 2017, 42(6): 431-440.)
Forensic error refers that the forensic conclusion itself and/or its reflecting arguments diverge from the reality. Forensic error consists of the errors amid the conclusions, those from producing, delivering, understanding and/or applying the conclusions since it can result from such various sources as instrument, method, bias and the artificial. According to the attribute, forensic error can also be of: 1) the false positive/negative conclusion in relation to source determination; 2) the unfaithful quantitative/qualitative assay in chemical detection; and 3) incorrect predicting opinions in evidence interpretation. Forensic error can occur in any one of all the stages of criminal justice from evidence-detecting/collecting in crime scene, evidence-packaging/preserving in transition, evidence-analyzing/interpreting in laboratory, report-writing and testimony-giving in conclusion-making until the conclusion-presenting/understanding in court. There are a lot of literatures that have been published in peer-reviewed journals about the empirical researches on validation and accuracy of forensic evidence. Although it is not possible to obtain a generally-accepted error rate reflecting real forensic casework by the empirical researches from the literatures, yet the acquired data do demonstrate that a risk of error really exists during forensic casework with the instances in identification of fingerprint, DNA, firearm, bite mark, handwriting and human hair, therefore capable of helping us understand the way and frequency of error occurrence so as to determine the weak spots and high-risk areas in forensic identification system.
[48]
王桂强. 物证鉴定错误减少对策研究[J]. 刑事技术, 2018, 43(1): 1-10.
摘要
物证鉴定若存在错误风险则会危害严重。恰当的物证鉴定错误管理可以有效减少物证鉴定错误的发生,有助于及时发现物证鉴定错误并将损害减至最小。本文探讨了在物证鉴定全部过程中有效管理物证鉴定错误的十二条措施:1)以有组织方式有条理的开展物证发现、提取、标记、记录、包装、保存和送检工作;2)持续强化物证鉴定科学基础研究和方法确认;3)在物证鉴定检验过程中实施多人平行鉴定、技术评审和管理审核程序;4)建立透明的鉴定意见冲突解决和鉴定结论表述机制;5)采用适当程序和方法有效管理和控制物证鉴定认知偏见信息;6)实施物证鉴定结论例行核查机制;7)建立检验留样和全面记录机制;8)有效评估物证鉴定结论错误风险;9)建立有效的用户培训和交流机制;10)及时发现和整改物证鉴定错误;11)构建物证鉴定科学文化;12)加强物证鉴定人培训。
(WANG Guiqiang. Strategies to mitigate forensic error[J]. Forensic Science and Technology, 2018, 43(1): 1-10.)
Forensic error, when existing and even causing risks, will do very likely a lot of harm to the criminal justice system. Suitable forensic error management can be effectively reducing the error generating, timely detecting the error, and even lowering the error-incurred damage to minimum. This article will inquire into the strategies to mitigate forensic error by implementing a dozen of relevant measures. 1) To systematically and orderly carry out evidence discovering, collecting, labeling, recording, packaging, preserving and submitting. 2) To continually strengthen the researches on forensic science basis and validation of methods used in forensic laboratory. 3) To adopt the procedures of paralleling multiple examiners, technical review and administrative evaluation. 4) To establish a transparent conflict-resolution policy for settling disagreements in technical decision from examiners. 5) To effectively manage and control the biasing information in forensic analysis. 6) To carry out the procedure of regularly checking cases files in order to search/avoid error. 7) To create and run a procedure of both retaining evidential samples and completely documenting the analytic process for renewing methods or peer review to assess the previous conclusion. 8) To evaluate the risk from forensic conclusion error. 9) To develop an effective mechanism for training and interchanging between forensic participators. 10) To timely detect/rectify forensic error. 11) To build up scientific culture among the forensic community. 12) To strengthen training and education of forensic examiners.
[49]
DROR I, KUKUCKA J. Linear sequential unmasking-expanded (LSU-E): a general approach for improving decision making as well as minimizing noise and bias[J]. Forensic Science International: Synergy, 2021, 3: 100161.

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