Judge Limits Evidence from Prosecutor Witness Based on Junk Science

Image from the California Innocence Project

By David M. Greenwald

Woodland, CA – Work on forensic evidence that has emerged from wrongful conviction cases, as well as the National Academy of Sciences, has cast serious doubt on the scientific backing of many so-called forensic techniques.

Responding to a motion from Public Defender Tracie Olson and her office, Judge David Reed, while denying the motion “to exclude all evidence of the similarities of markings on the bullets” relating to bullets found in West Sacramento and Richmond homicides, nevertheless agreed to “limit testimony of the similarities of the markings on the bullets.”

Alex Talfya, a prosecution witness, “will not be permitted to state that the bullets came from the same gun assuming no subclass influence as he did at the preliminary hearing.”

Judge Reed found, “That opinion is not supported by the facts or the science and misstates the level of scientific certainty of his findings and is therefore misleading.”

The judge will permit him to “describe the class characteristics he observed on the bullets” and “[t]he theory of toolmark analysis and how firearms leave markings on bullets or shell casing.”

He will also be allowed “to testify that he cannot exclude or eliminate the bullets as coming from different guns.”

However, “[H]e will not be permitted to describe any greater level of scientific certainty than the bullets may or may not have come from the same gun.”

On August 12, 2020, the defendant, Tuala Auimatagi, was held to answer on charges related to the murders of Errik Sanchez and Bruce Wayne Allen.

At that time, “Criminalist and firearms expert Alex Taflya testified that the bullets recovered from Mr. Allen and the bullet recovered from Mr. Sanchez were fired from the same firearm assuming no subclass influence.”

The defense brought forth a motion to exclude that testimony, requesting a Kelly hearing, regarding the admissibility of scientific evidence, on the belief that firearm and toolmark identification is not generally accepted in the scientific community.

The court permitted an evidentiary hearing on the validity of firearm and toolmark identification analysis, hearing from, among others, experts from the prosecution including Todd Weller, and defense experts Dean David Faigman and Dr. Nicholas Scurich.

Tracie Olson, representing Auimatagi, argued, “The prosecution, as the proponent of the evidence, has not met its burden under Kelly demonstrating that the firearm identification method used m this case is generally accepted by the scientific community, that the criminalist properly used valid techniques, that the proffered testimony is reliable under Sargon, and that the probative value of the testimony outweighs the prejudice that it will ensure, as required by Evidence Code section 352.”

She therefore argued that the court should limit the testimony of Taflya and “prohibit him from offering qualitative opinions on matters not adequately supported by the relevant scientific community.”

She argued that “Taflya may not opine on the signficance of any marks other than class characteristics consistent with the current state of the science with respect to identification and subclass.”

Further, she argued, “he should be instructed that he can only testify as to whether there is evidence of class characteristics, what those class characteristics are and whether the bullets recovered and examined were fired by the same class of firearm.”

In addition, “He should be instructed that he cannot state or imply a smaller subset of firearms as the possible source of the bullets other than those that share the same class characteristics.”

Likewise, “given the current state of the science, Mr. Taflya cannot be allowed to testify in subjective terms such as ‘sufficient agreement’ or ‘consistent with’ and certainly may not testify that the bullets recovered from the two autopsies were fired by the same gun, even with the caveat of assuming no subclass influence.

“These limitations accord with the evidence presented to this court,” she added.

In a motion filed by the Yolo County DA’s office, they argued that they “seek to introduce the testimony of Alex Taflya who will offer expert opinion based on training and experience and the degree of agreement of individual characteristics observed under the comparison microscope that the certain bullets were fired from the same firearm assuming no subclass influence.”

They argue, “Taflya does not state his expert opinion with any level of statistical certainty, much less 100% or absolute certainty and will not render his opinion ‘to the exclusion of all other firearms.’”

Weller, in his testimony, according to the prosecution, “indicated the relevant scientific community would be firearm and tool mark experts, forensic practitioners, and other scientists who have done research in the field. He opined that this relevant scientific community shares his opinion that firearm toolmark identification is valid.”

Defense expert Dean David Faigman referenced the 2008 National Academy of Science (NAS) Report, Assessing Feasibility, Accuracy and Technical Capability of a National Ballistics Database,” but, according to the prosecution, he acknowledged “that the 2008 report specifically stated that it was not a verdict on the underlying theory of firearm related tool marks nor a comment on the validity of the discipline.”

In his ruling, Judge Reed found that the cases cited by the defense and the evidence overall “does not support excluding all testimony of the similarities of the markings on the bullets.”  However, “the cases and the evidence do support limiting the opinions relating to the similarities.”

Judge Reed noted that the cases cited by the defense, including the the recent case of People v. Azcona ((2020) 58 Cal.App.3d 504) in California, “lead to the conclusion that the methodology, and the questionable foundational validity and analysis of error rates in the studies, do not support permitting opinions of a specific level of scientific certainty that bullets were fired from the same gun.

“Based on the methods used in this case, any opinion of the similarities of the markings of  the bullets is even weaker and less reliable than those made in other reported cases,” Judge Reed writes. “For instance, Taflya testified about similarities seen in grooves, not landings, on the bullets without evidence or evaluation of subclass or individual characteristics. Todd Weller, the prosecution expert, is quoted in the Ross case, that examiners are trained not to rely on groove impressions unless they have the gun (barrel) to rule out subclass characteristics.”

Here he notes, “Taflya did not do a subclass evaluation and did not have the gun to examine.”

Taflya used the CMS (consecutive matching striae) method of identification “which is used by a smaller segment of the forensic science community and seems to have no generally accepted standards.”

Judge Reed added, “The AFTE [Association of Firearm and Tool Mark Examiners] theory of identification requires ‘sufficient agreement’ between samples to identify them as coming from the same gun. The evidence did not support an opinion that the bullets had ‘sufficient agreement’ to come from the same gun.”

—David M. Greenwald reporting


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About The Author

The Vanguard Court Watch operates in Yolo, Sacramento and Sacramento Counties with a mission to monitor and report on court cases. Anyone interested in interning at the Courthouse or volunteering to monitor cases should contact the Vanguard at info(at)davisvanguard(dot)org - please email info(at)davisvanguard(dot)org if you find inaccuracies in this report.

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