Hope Star - Hope, AR
  • Scientist, NAS discredit CBLA

  • When Joe Louis Dansby, 61, of Redland in Nevada County, was convicted in 1997 of capital double homicide in the 1992 shooting deaths of a Nevada County couple, the forensic tool known as “Comparative Bullet Lead Analysis” was widely accepted as a valid evidentiary science, which played a key role in Dansby's conviction.
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  • When Joe Louis Dansby, 61, of Redland in Nevada County, was convicted in 1997 of capital double homicide in the 1992 shooting deaths of a Nevada County couple, the forensic tool known as “Comparative Bullet Lead Analysis” was widely accepted as a valid evidentiary science, which played a key role in Dansby's conviction. Based upon testimony by FBI Forensic Analyst Kathleen Lundy, spent bullet leads which were recovered from the victims were supposedly “matched” with bullet lead in unspent cartridges in a rifle owned by Dansby using the CBLA technique. As a result, Dansby has spent the last 16 years on Arkansas' Death Row, while other issues related to his conviction have been litigated on appeal. However, the issue of the “bullet match” asserted by Lundy has never been questioned. But, the concept of CBLA has since been completely discredited by William A. Tobin, a former FBI chief forensic metallurgist, and a report issued in 2004 by the National Academy of Sciences, which stemmed from a challenge by Tobin. Tobin retired in 1998 from the FBI Laboratory after 27 years as a supervisory special agent, and 24 years as a forensic metallurgist, during which he spent 12 years as chief forensic metallurgist, according to his biography as author of “Comparative Bullet Lead Analysis: A Case Study in Flawed Forensics,” which was published in The Champion magazine in July, 2004. Beginning in 1999, two years after Dansby's conviction in Miller County Circuit Court, Tobin began to question the science behind CBLA. Based upon Tobin's research, and the NAS study, the FBI no longer uses CBLA as a forensic tool. Tobin explained why in the aforementioned article, noting that it was a scientific tool which had no acceptable standards of verification, comparing it to the idea of testing the blood of the reader and himself and concluding both had the same parents. “The analytical (first) phase of this process is generally accepted in the medical and scientific communities and would not be challenged (in our comparison to CBLA),” he wrote. “However, a conclusion that, because the blood samples are of similar composition, therefore the reader and author have similar origins as to source (parents) is clearly an unjustifiable extrapolation.” Tobin says that kind of assumption has been ongoing in courtrooms with CBLA for 40 years. “When challenged as to the reliability of CBLA, practice advocates have typically addressed the general acceptance of the instrumentation and analytical procedure rather than scientific acceptability of the inferences drawn, and courts have admitted the practice as generally accepted in the scientific community, eventually allowing it to become a venerable forensic practice,” he wrote. But, judges have begun to see the difference. In a 2003 federal case, U. S. v. Ronald Mikos, the district Court wrote, “We understand that the FBI Laboratory has performed comparative bullet lead analysis (CBLA) for many years... In our opinion, however, the required standard of scientific reliability is met only as to the proposed opinion testimony that the elements composition of the bullets recovered from the body is indistinguishable from the composition of the bullets found in the Defendant's car. “There is no body of data to corroborate the government's expert's further opinion that from this finding it follows that the bullets must or even likely came from the same batch or melt,” the Court wrote. In an earlier case, U.S. v. Jenkins, in South Carolina in 1997, the Court in that instance questioned the ability of jurors to make proper assessments of probative value from CBLA testimony. “If he jury doesn't know how many bullets are out there like this and how big that melt was, how can they possibly consider this testimony and give it accurate probative value?” the Court wrote. “They are going to have to speculate as to how many people out there have got these bullets. I mean, it may be that everybody in Columbia (South Carolina) has got them.” The NAS study Tobin reviewed nine specific findings of the NAS study related to the FBI Laboratory, which concluded, in part, that additional studies are needed simply to compile verifiable data on bullet lead composition. Other findings noted that the FBI protocols for CBLA were not standardized to the extent that they could be used by other laboratories; a better statistical basis for bullet composition is needed; there is no standard, formal and comprehensive proficiency testing by which to qualify FBI bullet analysts; the FBI should publish its procedures and submit them to peer review; revisions of procedures in analysis should be consistent within the FBI Laboratory; and, the FBI should apply the same documented analytical protocol to all samples it receives, and should require analysts to follow that specific protocol in all cases. Tobin said the NAS study was conclusive of the point in several respects. “The Committee expressly indicated that available data do not support any statement that a crime scene bullet came from a particular box or boxes of ammunition, that the rate of laboratory error is unknown because the FBI Laboratory does not have a program of testing by an external agency that has been designed to assess the proficiency of its examiners, and that the FBI's internal testing program does not determine rate of error,” he wrote. The executive summary to the 2004 NAS report for the FBI takes away the certainty of expert testimony on what it terms “compositional analysis of bullet lead” (CABL) prior to 2004, characterizing it as “a reasonably accurate way of determining whether two bullets could have come from the same compositionally indistinguishable volume of lead (CIVL)...” But, the report is equivocal concerning the science, saying that it may prove useful in “appropriate cases” in providing corroborative evidence of guilt or exoneration. However, the summary does not define what may be “appropriate cases.” “CABL does not, however, have the unique specificity of techniques such as DNA typing to be used as standalone evidence,” the summary states. That statement stems from the acknowledgement by the NAS researchers that factors involved in bullet lead manufacture can create disparities in the distribution of leads across different manufacturing lots over time. “In practice, the detailed process followed by each manufacturer varies, and the process can vary even within a single manufacturer to meet demand,” the summary states. “For example, many bullet manufacturers add scrap lead from the bullet production to the melt at random times, sporadically changing the composition of the original melt. Likewise, the binning of bullets and cartridges may introduce more mixing of bullets from different melts. “In fact, the FBI's own research has shown that a single box of ammunition can contain bullets from as many as 14 distinct compositional groups,” the summary states. Legal interpretations As a result, the NAS has recommended that legal interpretations of CABL be defined by a range of possibilities, rather than the concept of a “match”, based, in part, upon the volume of variables involved. “However, the committee's review of the literature and discussions with manufacturers indicate that, because of variabilities in the manufacturing process, the amount of lead from a CIVL can range from the equivalent of as few as 12,000 to as many as 35 million 40-grain, .22 caliber longrifle bullets compared with a total of 9 billion bullets produced each year,” the summary states. Consequently, the summary states that, “Further, there is the possibility that bullets from different CIVLs may be analytically indistinguishable.” The summary states that among the findings of the report that testimony by analysts should be limited, as follows: --“The available data do not support any statement that a crime scene bullet came from a particular box of ammunition. In particular, references to 'boxes' of ammunition in any form should be avoided as misleading under Federal Rule of Evidence 403. --”Compositional analysis of bullet lead data alone also does not permit any definitive statement concerning the date of bullet manufacture. --”Detailed patterns of the distribution of ammunition are unknown, and as a result, experts should not testify as to the probability that the crime scene bullet came from the defendant. Geographic distribution data on bullets and ammunition are needed before such testimony can be given.” Next: Other cases.
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