REPORT TO THE PRESIDENT Forensic Science in Criminal Courts: Ensuring Scientific Validity of Feature-Comparison Methods Executive Office of the President President’s Council of Advisors on Science and Technology September 2016
The President’s Council of Advisors on No Science and Technology philosophers of science. Co-Chairs John P. Holdren Eric S. Lander Assistant to the President for President Science and Technology Broad Institute of Harvard and MIT Director, Office of Science and Technology Policy Vice Chairs William Press Maxine Savitz Raymer Professor in Computer Science and Honeywell (ret.) Integrative Biology University of Texas at Austin Members Wanda M. Austin Christopher Chyba President and CEO Professor, Astrophysical Sciences and The Aerospace Corporation International Affairs Princeton University Rosina Bierbaum S. James Gates, Jr. Professor, School of Natural Resources and John S. Toll Professor of Physics Environment, University of Michigan Director, Center for String and Roy F. Westin Chair in Natural Economics, Particle Theory School of Public Policy, University of University of Maryland, College Park Maryland Christine Cassel Mark Gorenberg Planning Dean Managing Member Kaiser Permanente School of Medicine Zetta Venture Partners v
Susan L. Graham Ed Penhoet Pehong Chen Distinguished Professor Emerita Director in Electrical Engineering and Computer Alta Partners Science Professor Emeritus, Biochemistry and Public University of California, Berkeley Health University of California, Berkeley Michael McQuade Barbara Schaal Senior Vice President for Science and Dean of the Faculty of Arts and Sciences Technology Mary-Dell Chilton Distinguished Professor of United Technologies Corporation Biology Washington University of St. Louis Chad Mirkin Eric Schmidt George B. Rathmann Professor of Executive Chairman Chemistry Alphabet, Inc. Director, International Institute for Nanotechnology Northwestern University Mario Molina Daniel Schrag Distinguished Professor, Chemistry and Sturgis Hooper Professor of Geology Biochemistry Professor, Environmental Science and University of California, San Diego Engineering Professor, Center for Atmospheric Sciences Director, Harvard University Center for Scripps Institution of Oceanography Environment Harvard University Craig Mundie President Mundie Associates Staff Ashley Predith Diana E. Pankevich Executive Director AAAS Science & Technology Policy Fellow Jennifer L. Michael Program Support Specialist vi
PCAST Working Group Working Group members participated in the preparation of this report. The full membership of PCAST reviewed and approved it. Working Group Eric S. Lander (Working Group Chair) Michael McQuade President Senior Vice President for Science and Broad Institute of Harvard and MIT Technology United Technologies Corporation S. James Gates, Jr. William Press John S. Toll Professor of Physics Raymer Professor in Computer Science and Director, Center for String and Integrative Biology Particle Theory University of Texas at Austin University of Maryland, College Park Susan L. Graham Daniel Schrag Pehong Chen Distinguished Professor Emerita Sturgis Hooper Professor of Geology in Electrical Engineering and Computer Professor, Environmental Science and Science Engineering University of California, Berkeley Director, Harvard University Center for Environment Harvard University Staff Diana E. Pankevich Kristen Zarrelli AAAS Science & Technology Policy Fellow Advisor, Public Policy & Special Projects Broad Institute of Harvard and MIT Writer Tania Simoncelli Senior Advisor to the Director Broad Institute of Harvard and MIT vii
Senior Advisors PCAST consulted with a panel of legal experts to provide guidance on factual matters relating to the interaction between science and the law. PCAST also sought guidance and input from two statisticians, who have expertise in this domain. Senior advisors were given an opportunity to review early drafts to ensure factual accuracy. PCAST expresses its gratitude to those listed here. Their willingness to engage with PCAST on specific points does not imply endorsement of the views expressed in this report. Responsibility for the opinions, findings, and recommendations in this report and for any errors of fact or interpretation rests solely with PCAST. Senior Advisor Co-Chairs The Honorable Harry T. Edwards Jennifer L. Mnookin Judge Dean, David G. Price and Dallas P. Price United States Court of Appeals Professor of Law District of Columbia Circuit University of California Los Angeles Law Senior Advisors The Honorable James E. Boasberg The Honorable Pamela Harris District Judge Judge United States District Court United States Court of Appeals District of Columbia Fourth Circuit The Honorable Andre M. Davis Karen Kafadar Senior Judge Commonwealth Professor and Chair United States Court of Appeals Department of Statistics Fourth Circuit University of Virginia David L. Faigman The Honorable Alex Kozinski Acting Chancellor & Dean Judge University of California Hastings College of United States Court of Appeals the Law Ninth Circuit Stephen Fienberg The Honorable Cornelia T.L. Pillard Maurice Falk University Professor of Statistics Judge and Social Science (Emeritus) United States Court of Appeals Carnegie Mellon University District of Columbia Circuit viii
The Honorable Charles Fried The Honorable Jed S. Rakoff Beneficial Professor of Law District Judge Harvard Law School United States District Court Harvard University Southern District of New York The Honorable Nancy Gertner The Honorable Patti B. Saris Senior Lecturer on Law Chief Judge Harvard Law School United States District Court Harvard University District of Massachusetts ix
Executive Summary “Forensic science” has been defined as the application of scientific or technical practices to the recognition, collection, analysis, and interpretation of evidence for criminal and civil law or regulatory issues. Developments over the past two decades—including the exoneration of defendants who had been wrongfully convicted based in part on forensic-science evidence, a variety of studies of the scientific underpinnings of the forensic disciplines, reviews of expert testimony based on forensic findings, and scandals in state crime laboratories— have called increasing attention to the question of the validity and reliability of some important forms of Main conclusions: forensic evidence and of testimony based upon them. 1 A multi-year, Congressionally-mandated study of this issue released in 2009 by the National Research Council 2 two important gaps: ( Strengthening Forensic Science in the United States: A Path Forward ) was particularly critical of weaknesses in (1) the need for clarity about the scientific underpinnings of a number of the forensic disciplines routinely used in the criminal justice system. That report led to extensive discussion, inside and outside the Federal government, of a path forward, and the scientific standards for ultimately to the establishment of two groups: the National Commission on Forensic Science hosted by the the validity and reliability of Department of Justice and the Organization for Scientific Area Committees for Forensic Science at the National Institute of Standards and Technology. forensic methods When President Obama asked the President’s Council of Advisors on Science and Technology (PCAST) in 2015 to consider whether there are additional steps that could usefully be taken on the scientific side to strengthen the and forensic-science disciplines and ensure the validity of forensic evidence used in the Nation’s legal system, PCAST concluded that there are two important gaps: (1) the need for clarity about the scientific standards for the (2) the need to evaluate validity and reliability of forensic methods and (2) the need to evaluate specific forensic methods to determine whether they have been scientifically established to be valid and reliable. specific forensic methods to determine whether they This report aims to help close these gaps for the case of forensic “feature-comparison” methods—that is, methods that attempt to determine whether an evidentiary sample (e.g., from a crime scene) is or is not have been scientifically associated with a potential “source” sample (e.g., from a suspect), based on the presence of similar patterns, established to be valid and impressions, or other features in the sample and the source. Examples of such methods include the analysis of reliable. DNA, hair, latent fingerprints, firearms and spent ammunition, toolmarks and bitemarks, shoeprints and tire tracks, and handwriting. 1 Citations to literature in support of points made in the Executive Summary are found in the main body of the report. 2 The National Research Council is the study-conducting arm of the National Academies of Science, Engineering, and Medicine. 1
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