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Maryland Supreme Court: Firearms Identification Methodology Does Not Provide Reliable Basis for Expert’s Unqualified Opinion That Bullets Recovered at Crime Scene Were Fired From Defendant’s Gun

by Douglas Ankney

The Supreme Court of Maryland (formerly known as the Court of Appeals of Maryland) held that the methodology of firearms identification presented to the trial court did not provide a reliable basis for the expert witness’ unqualified opinion that four bullets and one bullet fragment found at the crime scene were fired from the defendant’s gun.

Kobina Ebo Abruquah was tried a second time by jury for the murder of his roommate, Ivan Aguirre-­Herrera, after his first judgment was reversed and remanded for a new trial by the Appellate Court of Maryland (formerly known as the Court of Special Appeals). Aguirre-­Herrera was shot five times. Police recovered four bullets and two bullet fragments from the crime scene. (Only one of the fragments was later determined to be suitable for testing.)

During the investigation, Abruquah told police that he owned two firearms – a Glock pistol and a Taurus .38 Special revolver. Police recovered both firearms from the home shared by the two men. At trial on remand, the State’s expert witness and firearm examiner Scott McVeigh opined – over defense counsel’s objection – that the four bullets and one of the bullet fragments recovered from the crime scene “at some point had been fired from [the Taurus revolver].”

Abruquah was again convicted of first-­degree murder and related handgun offenses. He appealed to the Appellate Court, and while that appeal was pending, the Maryland Supreme Court granted certiorari to Abruquah on the question of “whether the firearms identification methodology employed by Mr. McVeigh is sufficiently reliable to allow a firearms examiner, without any qualification, to identify a specific firearm as the source of a questioned bullet or cartridge case found at a crime scene.”

The Court observed that trial courts “analyzing the admissibility of evidence under Rule 5-­702 are to consider the following non-­exhaustive list of factors in determining whether the proffered expert testimony is sufficiently reliable to be provided to the trier of facts:

(1) whether a theory or technique can be (and has been) tested;

(2) whether a theory or technique has been subjected to peer review and publication;

(3) whether a particular scientific technique has a known or potential rate of error;

(4) the existence and maintenance of standards and controls; …

(5) whether the theory is generally accepted[;] …

(6) whether experts are proposing to testify about matters growing naturally and directly out of research they have conducted independent of the litigation, or whether they have developed their opinions expressly for purposes of testifying;

(7) whether the expert has unjustifiably extrapolated from an accepted premise to an unfounded conclusion;

(8) whether the expert has adequately accounted for obvious alternative explanations;

(9) whether the expert is being as careful as [the expert] would be in [the expert’s] paid litigation consulting; and

(10) whether the field of expertise claimed by the expert is known to reach reliable results for the type of opinion the expert would give.” Rochkind v. Stevenson, 236 A.3d 630 (Md. 2020). These 10 factors are referred to as the “Daubert-­Rochkind factors.”

After reviewing other relevant guidance in determining the admissibility of expert witness testimony, the Court advised that the “overarching criterion for the admission of relevant expert testimony … is reliability.” This does not mean that trial courts are to evaluate whether the proposed expert testimony is right or wrong but rather that it “meets a minimum threshold of reliability,” according to the Court.

The Association of Firearm and Toolmark Examiners’ (“AFTE”) “Theory of Identification” (“AFTE Theory”) – the most commonly used methodology by firearm examiners – was the methodology used in the present case.

The AFTE Theory relies on the premise that firearms imprint unique markings onto bullets and cartridge casings when the bullets are fired and that these markings on the bullets and casings can be used to determine whether a particular weapon fired the bullet and/or left the spent casing. The AFTE Theory of examination requires the examiner to first determine the “class characteristics” of the bullets and/or casings recovered from the crime scene (“unknown samples”). Class characteristics include caliber of weapon, lands, grooves, and direction of twist. If the class characteristics of the unknown samples do not agree with the bullets and/or casings test fired from the suspected weapon (“known samples”), the firearm is excluded as the source of the unknown samples.

But if the class characteristics agree, the examiner compares the known and unknown samples under a comparison microscope. The examiner then engages in “pattern matching” to determine whether any markings are “subclass” (markings common to several weapons of the same class due to a tool misaligned during manufacturing or similar unique factor) or “individual markings” (microscopic markings unique to a firearm caused by slight variations during the manufacturing of each firearm, the use of the firearm, cleaning and maintenance of the firearm, etc.). Notably, the Court observed that “not all individual characteristics are unique … and individual characteristics can change over the life of a firearm as a result of, for example, wear, polishing, or damage.”

Based on the foregoing “pattern matching,” the examiner then makes a determination in accordance with the options set forth in the “AFTE Range of Conclusions”:

1. “Identification” occurs when there is agreement “of a combination of individual characteristics and all discernible class characteristics where the extent of agreement exceeds that which can occur in the comparison of toolmarks made by different tools and is consistent with the agreement demonstrated by toolmarks known to have been produced by the same tool.”

2. The three categories of “Inconclusive” (all of which require full agreement of “all discernible class characteristics”) are: (a) when there is some “agreement of individual characteristics … but insufficient for an identification”; (b) when there is neither “agreement [n]or disagreement of individual characteristics”; and (c) when there is “disagreement of individual characteristics, but insufficient for an elimination.”

3. “Elimination” occurs when there is significant “disagreement of discernible class characteristics and/or individual characteristics.”

The Court pointedly stated that the AFTE acknowledges that “the interpretation of individualization/identification is subjective in nature.” Furthermore, the AFTE Theory lacks “objective criteria” in determining what constitutes the “best agreement demonstrated” between toolmarks made by different tools or what satisfies “quantity and quality” of agreement demonstrating a “practical impossibility” of a different tool being responsible for making the same mark. Finally, the Court observed that there “are also no established standards for classifying a particular pattern or mark as a subclass versus an individual characteristic.”

The Court reviewed the circuit court’s conclusions as to all 10 of the Daubert-­Rochkind factors. But factors (3), (4), (7), and (8) were dispositive of the issue raised in the question for review, according to the Court.

Regarding factor (3), the Court observed that the calculated error rates in two studies – Ames I and Ames II – “were in the low single digits.” In Ames I, “15 sets of four cartridges fired from 25 new, same-­model handguns using the same type of ammunition were sent to 218 examiners. Each set included one unknown sample and three known samples fired from the same known gun, which might or might not have been the source of the unknown sample. Even though there was a known correct answer of either an identification or an elimination for every set, examiners were permitted to make ‘inconclusive’ responses, which were ‘not counted as an error or as a non-­answer.’”

In Ames II, 173 examiners were enrolled in a three-­phase study. In each phase, the “examiner received 15 comparison sets of known and unknown cartridge cases and 15 comparison sets of known and unknown bullets.” As with Ames I, even though there was a correct answer of either identification or elimination, the “examiners were permitted to pick from among the full array of the AFTE Range of Conclusions – identification, elimination, or one of the three levels of ‘inconclusive.’”

“In Phase 1, the examiners were tested for accuracy. They were asked to identify a known match or eliminate a known nonmatch. In Phase 2, examiners were tested for repeatability – defined as “the ability of an examiner, when confronted with the exact same comparison once again, to reach the same conclusion as when first examined.” Without being told, the examiners were given the same test set as given in Phase I to determine if the examiners would reach the same conclusions. Finally, in Phase 3, the examiners were given a test set previously examined by a different examiner to test reproducibility – defined as “the ability of the second examiner to evaluate a comparison set previously viewed by a different examiner and reach the same conclusion.” 

The Court observed that the calculated error rates did not count the answer “inconclusive” as incorrect. In Ames I, when examiners compared bullets or cases from different sources, they made a finding of “inconclusive” 33.7 % of the time. In Ames II, examiners made a finding of “inconclusive” in more than 65% of the samples that were from different sources and in more than 20% of the samples from same sources. This demonstrated that examiners resorted to “inconclusive” because they knew it would not be counted as a wrong answer. If just the Phase I “inconclusive” findings for nonmatching bullets in Ames II were counted as “incorrect” (that is, the examiner “almost” made an incorrect positive identification but opted for inconclusive), the error rate ballooned from 0.7% to 10.13%. Therefore, the reported low error rates are unreliable, the Court determined.

As to factor (4), a witness for the State testified that an examiner’s identification must be verified by another examiner. However, in actual case work, the second examiner is made aware of the first examiner’s conclusions. The witness also testified that in his decades of experience working in laboratories in multiple states, “he was not aware of a single occasion in which a second reviewer had reached a different conclusion than the first.” Yet in Phase III of Ames II, when the second examiner was not informed of the results of the first examiner, the second examiner classified matching sets in the same AFTE category as the first examiner less than 70% of the time and for nonmatching sets it was less than 41% of the time.

Regarding factor (7), the Court observed an “analytical gap typically occurs as a result of the failure by the expert witness to bridge the gap between [the expert’s] opinion and the empirical foundation on which the opinion was derived.” State v. Matthews, 277 A.3d 991 (Md. 2022). At a pretrial hearing, McVeigh “rejected the notion that a firearms examiner looking at a bullet multiple times might come to different conclusions.” But Phase II of Ames II established that “an examiner reviewing the same bullet set a second time classified it in the same AFTE category only 79% of the time for matching sets and 65% of the time for nonmatching sets.” Without any objective criteria for determining which markings are “individual,” and without any objective guidance as to how many such markings must be “in agreement” to support an “identification,” the AFTE Theory is not a methodology upon which “to reliably opine without qualification that the bullets of unknown origin were fired from a particular firearm,” the Court declared.

Finally, as to factor (8), the Court reasoned “without the ability to examine other bullets fired from other firearms in the same production run as the firearm under examination, the record simply does not support that firearms identification can reliably eliminate all alternative sources so as to permit unqualified testimony of a match between a particular firearm and a particular crime scene bullet.”

The Court explained that “based on … the lack of evidence that study results are reflective of actual casework, firearms identification has not been shown to reach reliable results linking a particular unknown bullet to a particular known firearm.” It further explained that “the methodology of firearm identification presented to the circuit court did not provide a reliable basis for Mr. McVeigh’s unqualified opinion that four bullets and one bullet fragment found at the crime scene in this case were fired from Mr. Abruquah’s Taurus revolver. In effect, there was an analytical gap between the type of opinion firearms identification can reliably support and the opinion Mr. McVeigh offered.”

Thus, the Court held that the circuit court did not abuse its discretion in allowing McVeigh to testify about firearms identification in general, his examination of the bullets and bullet fragments recovered from the crime scene, his comparison of that evidence with bullets fired from Abruquah’s Taurus firearm, and “whether the patterns and markings on the crime scene bullets are consistent or inconsistent with the patterns and markings on the known bullets.” However, the Court further held that the circuit court did abuse its discretion by allowing the State’s expert witness “to opine without qualification that the crime scene bullets were fired from” Abruquah’s Taurus firearm.

Accordingly, the Court reversed and remanded for a new trial. See: Abruquah v. State, 296 A.3d 961 (Md. 2023).  

Editor’s note: Anyone with an interest in firearms identification is strongly encouraged to read the Court’s full opinion, which includes an excellent discussion of the serious flaws in the forensic technique’s genuine ability to identify a specific firearm as the source of a specific ammunition component revealed by the major studies on the issue. It also includes an informative roundup of the current case law from various jurisdictions on the topic of admissibility and the scope of expert witness testimony on firearms identification.

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