Statistics, Department of


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VanderPlas, Khan, Hofmann, & Carriquiry (2022) Reply to Response by FBI Laboratory filed in Illinois v. Winfield and Affidavit by Biederman et al. (2022) filed in US v. Kaevon Sutton (2018 CF1 009709). Filed by the defense in Illinois v. Winfield (15 CR 14066-01)

doi: 10.32873/unl.dc.oth.018


Copyright 2022, the authors. Used by permission.


1 Preliminaries

1.1 Scope

The aim of this document is to respond to issues raised in Federal Bureau of Investigation1 and Alex Biedermann, Bruce Budowle & Christophe Champod.2

1.2 Conflict of Interest

We are statisticians employed at public institutions of higher education (Iowa State University and University of Nebraska, Lincoln) and have not been paid for our time or expertise when preparing either this response or the original affidavit.3 We provide this information as a public service and as scientists and researchers in this area.

1.3 Organization

The rest of the document precedes as follows: we begin by outlining our main points of agreement with the Federal Bureau of Investigation4 (hereafter, FBI) and Biedermann, Budowle, and Champod5 (hereafter, BBC) in Section 2. As a threshold issue, we consider the concept of a general discipline-wide error rate in Section 3 in order to correct statistical misconceptions in Biedermann, Budowle, and Champod.6 We then describe the statistical concepts underlying our assessment of the discipline of firearms and toolmark examiners in Section 4. Finally, we address specific issues with participant and material sampling (Section 5), study design (Section 6), and the use of inconclusives (Section 7).

1 FBI Laboratory Response to the Declaration Regarding Firearms and Toolmark Error Rates Filed in Illinois v. Winfield (Aff. filed in US v Kaevon Sutton dated May 3, 2022).

2 Forensic feature-comparison as applied to firearms examinations: evidential value of findings and expert performance characteristics (Aff. filed in US v Kaevon Sutton dated April 28, 2022).

3 Susan Vanderplas et al., Firearms and Toolmark Error Rates (Aff. filed in Illinois v Winfield, January 2022).

4 Supra note 1.

5 Supra note 2.

6 Supra note 2.