Assessing Relevance of Information for Forensic Service Providers, Summaries of Law

Download Assessing Relevance of Information for Forensic Service Providers and more Summaries Law in PDF only on Docsity! 1 NATIONAL COMMISSION ON FORENSIC SCIENCE Ensuring That Forensic Analysis Is Based Upon Task-Relevant Information Subcommittee Human Factors Type of Work Product Views Document Statement of the Issue: What is the proper evidentiary basis for a forensic science opinion? In other words, what facts should forensic science service providers (FSSPs) consider and what facts should they not consider when drawing conclusions from physical evidence? These are questions of fundamental importance to forensic science. The need for clear answers has become increasingly important as FSSPs are being called on to address the challenge of contextual bias. It is the view of the National Commission on Forensic Science that: 1. FSSPs should rely solely on task-relevant information when performing forensic analyses. 2. The standards and guidelines for forensic practice being developed by the Organization of Scientific Area Committees (OSAC) should specify what types of information are task-relevant and task-irrelevant for common forensic tasks. 3. Forensic laboratories should take appropriate steps to avoid exposing analysts to task-irrelevant information through the use of context management procedures detailed in written policies and protocols. 1 – Pertinent Principles This document sets forth principles that FSSPs should use to assess the relevance of information to specific forensic tasks. It uses the term task-relevant to describe information that FSSPs should consider when performing a particular task; it uses the term task-irrelevant to describe information that should not be considered. When discussing what is task-relevant, it is useful to distinguish three phases at which forensic FSSPs may be involved in a criminal investigation. There is often a preliminary phase, in which FSSPs survey a crime scene, decide what evidence to collect, and determine what examinations are needed. This is followed by an analytic phase, during which specific items of evidence are examined, analyzed, and compared. This may be followed by an evaluative phase, in which FSSPs help police and lawyers understand the implications of the analytic findings and put them in context. Evidence that is task-relevant during the evidence collection and evaluative phases may not be task- relevant during the analytic phase. For example, statements of witnesses about what happened during a crime may be task-relevant when deciding what evidence to collect at a crime scene or what examinations 2 are needed. Such statements may also be task-relevant when making an overall assessment of the case in light of the forensic evidence. But witness statements generally are not relevant to the task of interpreting analytic tests. The results of analytic examinations and comparison should depend on the physical evidence examined, not on what witnesses say. What is relevant to a particular forensic task will also depend on the propositions the FSSP is asked to assess. As used here, the term proposition refers to a theory or hypothesis about the event in question that a FSSP is asked to assess (Cook et al., 1998). FSSPs are often asked to assess propositions about the source of an item. They might be asked, for example, to assess whether a biological specimen came from a suspect or from someone else, or whether a shell casing was fired by a particular gun rather than by some other gun. FSSPs might also be asked to assess propositions about the activity that produced a particular item of evidence. For example, bloodstain pattern analysts might be asked whether a particular bloodstain was produced by a high-velocity impact, by arterial bleeding, or by expiration (coughing) (Kish et al., 2005; Laber et al., 2014). When performing analytic tasks, FSSPs should draw conclusions solely from the physical evidence that they are asked to evaluate (along with any task-relevant context), and not from any other evidence in the case. Fingerprint examiners should draw conclusions from fingerprints, tool mark examiners from tool marks, DNA experts from biological evidence. It would be inappropriate, for example, if analytic conclusions were influenced by whether the suspect made incriminating statements or had a criminal record, or whether other forensic evidence implicated the suspect. Those are matters to be considered by police, prosecutors, and jurors, not matters that should influence a scientific assessment of evidence. FSSPs should base their conclusions on methods that are accepted as valid within their specific disciplines. They should draw conclusions only from methods or techniques that they are trained and competent to use. From these considerations, it follows that information is task-relevant for analytic tasks if it is necessary for drawing conclusions: (i.) about the propositions in question, (ii.) from the physical evidence that has been designated for examination, (iii.) through the correct application of an accepted analytic method by a competent analyst. Information is task-irrelevant if it is not necessary for drawing conclusions about the propositions in question, if it assists only in drawing conclusions from something other than the physical evidence designated for examination, or if it assists only in drawing conclusions by some means other than an appropriate analytic method. As previously indicated, FSSPs will sometimes need contextual information in order to perform a particular task. For example, a fingerprint examiner may need information about the surfaces from which the prints were lifted in order to assess whether discrepancies between prints could have been caused by curvature or distortion of one of the surfaces. A bloodstain pattern analyst may need information about the location of the blood in order to assess various propositions about how it was deposited. The test of whether such ancillary contextual information is relevant to a forensic assessment is whether it helps the examiner draw an accurate forensic conclusion from the physical evidence designated for testing using accepted methods. It is task-relevant if it helps the analyst assess the strength of the inferential connection between the physical evidence being examined and the propositions the analyst is evaluating. But contextual information often supports inferences about a proposition only through a chain of logic that does not involve assessment of the physical evidence. Contextual information of this type is task- 5 A second approach is to design the workflow in the laboratory in a manner that assures that analysts make critical assessments before they become aware of potentially biasing information. This strategy is helpful in instances in which information that is irrelevant for some tasks is relevant and necessary for other tasks that are performed by the same analyst. For example, information about the DNA profile of a suspect is irrelevant and potentially biasing when a DNA analyst is attempting to determine what genotypes are present in an evidentiary profile (Dror & Hampikian, 2011; Thompson, 2009), but is necessary and relevant when the analyst evaluates whether the suspect could be a contributor to the DNA in the evidentiary profile. To reduce the potential for bias in DNA testing, some laboratories require analysts to follow a procedure known as “sequential unmasking” (Krane, et al., 2008; Dror, et al., 2015), in which evidentiary samples from crime scenes are typed and interpreted before analysts learn of the profiles of any known or suspected contributors. The DNA profiles of known contributors and possible suspects are then “unmasked” in a specific sequence to minimize the likelihood that information about the reference profiles will influence interpretation of the evidentiary samples. This procedure has been adopted successfully by the Netherlands Institute of Forensic Sciences (Stoel, et.al., 2015). Similar procedures have been recommended by the Expert Working Group on Human Factors in Latent Print Analysis (2012) and have been adopted by laboratories in the United States. For example, the FBI laboratory has reportedly adopted a similar procedure for latent print analysis, as has the Virginia Department of Forensic Science and the Minnesota Bureau of Criminal Apprehension. Called “linear ACE-V,” the FBI’s procedure involves temporary masking of reference prints while analysts make and record their initial assessments of the evidentiary prints (Office of the Inspector General, Department of Justice, 2011). 1 Many laboratories have adopted computerized Laboratory Information Management Systems (LIMS), in which case files, laboratory notes, and other records are maintained. These systems can and should be programmed to facilitate context management by preventing analysts from premature access to potentially biasing task-irrelevant information (e.g., by preventing bench-level analysts from accessing witness statements and police reports until after they complete their evaluations of evidentiary samples). Those developing such systems should pay careful attention to what information is task-relevant at various stages in the laboratory process and should cooperate with forensic laboratories to assure that the appropriate information is available when needed. Forensic laboratories should begin to implement context management procedures. As they do so, they should systematically monitor laboratory performance in order to identify strengths and weaknesses of the new procedures, document unanticipated consequences, and learn from trial and error which context management procedures are most successful and practical. 1 The acronym ACE-V designates four critical steps of latent print analysis: analysis, comparison, evaluation, and verification. 6 References Cook, R., Evett, I.W., Jackson, G., Jones, P.J., & Lambert, J.A. (1998). A hierarchy of propositions: deciding which level to address in casework. Science & Justice, 38. Dror, I.E., & Charlton, D. (2006). Why experts make errors. 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