in Firearms/Toolmarks Forensic Practice

Transcription

1 Hypothesis Testing of the Critical Underlying Premise of Discernible Uniqueness in Firearms/Toolmarks Forensic Practice 53 Jurimetrics J., (2013) William A. Tobin Peter J. Blau (804)

2 Hypothesis Testing of the Critical Underlying Premise of Discernible Uniqueness in Firearms/Toolmarks Forensic Practice 53 Jurimetrics J., (2013) Abstract: Firearms/Toolmarks forensic practice rests on indefensible conceptual foundation of discernible uniqueness of firearms & tools. Similar to now-defunct practice of bullet lead analysis (CBLA), there does not exist any scientifically acceptable hypothesis testing of underlying premises. Existing studies are pervasively and fatally flawed and are largely irrelevant to individual criminal cases.

3 Typical firearms identification examiner testimony: The questioned bullet/cartridge case was fired from/in the [suspect s] pistol

4 AFTE Theory of Identification 1. Theory of identification enables opinions of common origin when the unique surface contours of two toolmarks are in sufficient agreement 2. Agreement is sufficient when there is enough similarity to opine an identification in the subjective experience of the examiner

5 Critical Premises Discernible uniqueness (examiner can detect individuality of each firearm) Repeatability* (characteristics imparted by firearm are nonvolatile; characteristics imparted during fabrication are volatile) * Not discussed in detail in this paper

6 Critical Premises Discernible uniqueness - intuited - no comprehensive or meaningful studies - no protocol: - no parameters of detection - no rules of application Repeatability - assumed in firings - summarily dismissed in manufacturing

7 AFTE Theory of Identification Not scientific protocol Uses circular reasoning: ID allowed when sufficient agreement exists sufficient agreement defined as enough agreement for ID Fallacy of Presumption: enables opinions of common origin to be made when the unique surface contours of two toolmarks are in sufficient agreement.

8 Specific source attributions are inherently probabilistic (statistical)

9 Claims Denying Use of Statistics Assertion: Forensic identification doesn t use statistics Reality: Claims of individualization: inherently probabilistic. Probability scale range: 0 (impossibility) to 1 (certainty) Claim of individualization implies probability of 1

10 There is no basis for any claim of certainty, including specific source attribution (individualization)

11 Proficiency Tests & Validation Studies Proficiency Tests: numerous flaws, including Do not mirror real-world case work Neither double-blind nor blind Inconclusive opinions not counted Rate of inconclusives rises dramatically during testing Laughably easy (per Scotland Yard firearms examiner supervisor) No control over collaborative efforts Samples provided in pristine condition Samples pre-screened to insure clarity of characteristics Purported Validation Studies Largely irrelevant to specific case at bar Contain numerous fallacies of presumption, including suppressed evidence, false dichotomy, petitio principii Don t measure what they represent to test

12 Error Rates Formerly claimed to be infallible, rates of practice error are MUCH higher than the typical 0 to 1% now asserted

13 2.3% (#2: 3/130) Lowell Bradford, Forensic Firearms Identification: Competence or Incompetence?, AFTE J., Vol.2, No.2, Apr % (#2 test (5/132) reported by Bradford, correction of), Thornton, J, Nationwide Crime Lab Proficiency Project, AFTE J., Vol.2, No.2 (Apr. 1979) 5.7% misidentifications; Lowell Bradford & John Thornton, no disagreement (see both Bradford & Thornton articles cited here); probably referring to LEAA testing (see 28.2% comments, below) 3-8% Peterson, Markham, Crime Laboratory Proficiency Testing Results, , II: Resolving Questions of Common Origin, J.For.Sci., (1995), at % (#3-5/57) Lowell Bradford, Forensic Firearms Identification: Competence or Incompetence?, AFTE J., Vol.2, No.2, Apr % clearly in error (excludes inconclusives ): Randolph Jonakait, Forensic Science: The Need for Regulation, Harvard J. of Law & Tech, Vol. 4, Spring 1991 at 111, citing LEAA rept of Peterson, Fabricant & Field, Crime Laboratory Proficiency Testing Research Program 26 (1978), at % Detroit PD Firearms Unit, Prelim.Audit Findings as of Sept.23, 2008, Rept. of MSP For.Sci.Div: available at: 12% Peterson & Markham (1995), Crime Lab Prof.Tstg Results II, J.ForSci 1009, et al. 24% 28% unacceptable results as misidentifications, Lowell Bradford, Forensic Firearms Identification: Competence or Incompetence?, AFTE J., Vol.2, No.2, Apr. 1979, poss. referring to LEAA testing, below 28.2% unacceptable results, include wrong outcomes, Type 3 errors, inconclusive unsupported by analytical results

14 Hypothesis Testing of the Critical Underlying Premise of Discernible Uniqueness in Firearms/Toolmarks Forensic Practice 53 Jurimetrics J., (2013) William A. Tobin Peter J. Blau (804)