Author's response

The William Campbell case involved an automobile accident that resulted in a death and criminal legal proceedings across three trials and 12 years [1]. The Campbell case included six forensic examinations that were coded in the wrongful convictions study, including forensic pathology, DNA, crime scene investigation, accident reconstruction, chemical analysis of fire debris, and hair comparison. One of the corresponding authors of the letter, Mr. Trimpe, testified concerning the hair comparison and provided a statement concerning the uniqueness of hair based on his personal experience during his career. As in all cases in the research study, the hair comparison testimony was assessed for conformance to standards in place at the time of trial and standards in place at the time of the study's initiation [2, 3]. Although the testimony appears to have conformed to standards in place in 2009 (the time of trials 1 and 2), the testimony would not conform to the standards of the Department of Justice's Uniform Language for Testimony and Reports (ULTR), which was clearly stated in the original paper as the basis for assessment of hair testimony currently [3]. The ULTR's prohibit the citation of personal experience “as a direct measure for the accuracy of a proffered conclusion.” The hair testimony was not coded as “required for conviction” because it was not dispositive with respect to the interpretation of the accident reconstruction. These details were not provided in the paper because it was impossible to provide context for every coding decision across the 732 cases in the study nor was it possible to list the over 6000 documents that were used to inform case coding, as was outlined in the original paper. The Campbell case provides key insights for forensic science improvement. As discussed in the original paper, the case was unusual for the post-2000 period in that hair comparison was presented without confirmation by DNA. By the time of the initial trial in 2009, the error rate of hair comparison and the need for DNA confirmation were well-established [4]. The hair comparison testimony was similar to that given by many FBI examiners in the past, including the statement using personal experience as a basis for the accuracy of hair comparison [5]. Otherwise, the hair comparison appears to have been completed extremely well in the Campbell case, just as it was in many of the cases that were the subject of the FBI's review of hair comparisons. Nonetheless, forensic testimony must conform to appropriate standards in all respects, not just most of the time. This issue is not merely of academic interest. The correspondents hold that it is unreasonable to hold that such statements imply individualization, but some courts disagree and are increasingly critical of the language of forensic testimony. For example, the Maryland Supreme Court recently ruled that an examiner should not be permitted to “offer an unqualified opinion that crime scene bullets and a bullet fragment were fired from the petitioner's gun [6].” This means that Maryland firearms examiners will be constrained to use descriptive testimony similar to the hair testimony provided in the Campbell case. The Maryland opinion and others like it are not based solely on concerns about the scientific reliability of pattern evidence disciplines. They also recognize that pattern evidence disciplines remain vulnerable to examiner subjectivity. Hence, they seek to limit conclusion statements and other testimony that could improperly be construed to imply individualization on the basis of an examiner's experience or opinion. The requirements of the ULTR standard also reflect these concerns [7]. Forensic examiners should demand the development and enforcement of science-based standards that are recognized by the courts in a predictable and uniform way. Just as importantly, forensic science organizations should reject a blame-first mentality when errors occur. Instead, we should consider root causes and seek to implement useful solutions to mitigate the risk of future errors. In this spirit, the correspondents should consider that the wrongful convictions research study was not intended to highlight any fault by Mr. Trimpe in particular, but rather to use the case as a learning opportunity to highlight the importance of rigorous, science-based testimony standards.