People v. Cowan, 236 P.3d 1074 (Cal. 2010)

Method used by expert: Laskowski testified that in 1984 he had excluded the Colt pistol as the source of the bullets recovered from Clifford’s body based on a comparison of those bullets with test-fired bullets. A few weeks before trial, however, Detective Christopherson had informed him that the inside of the barrel had been altered. Laskowski reexamined the gun and determined that the land impressions near the crown of the barrel had been damaged to such an extent that comparison with test-fired bullets was impossible. Laskowski therefore made a cast of the interior of the barrel using Mikrosil, a silicone rubber compound routinely used in the casting of tool marks. He then compared the markings on the cast that had been recorded from the inside of the barrel with the two bullets recovered from Clifford’s body, and determined the bullets had been fired from the Colt pistol.

On cross-examination, Laskowski admitted that neither he nor any other ballistics expert he was aware of had ever testified in court regarding ballistics comparisons using Mikrosil casting. However, at least a dozen or more experts he had spoken with told him that the method was “acceptable.” Moreover, he explained, the technique was not new, because “the recording of tool marks with an elastomeric material has been done,” and firearms examination was essentially a subset of tool mark comparison.

At the Evidence Code section 402 hearing and at trial, Laskowski explained in detail the process he had used to create the barrel cast and compare it to the bullets recovered from Clifford Merck’s body. Laskowski showed photographs of the gun, the barrel cast, the test-fired bullets and the recovered bullets to the jury and identified the points of similarity he found between the cast and the recovered bullets. Although there was some dispute about whether the method Laskowski used produced a cast of the barrel “without tampering or alteration” due to possible bubbling or shrinkage of the Mikrosil, that possibility was fully explored on cross-examination and the jury had the opportunity to weigh its effect on the validity of Laskowski’s conclusions. Thus, here too there was no need to debate the reliability of the method under the standards of Kelly.

Kelly rule: The Kelly rule provides that the “admissibility of expert testimony based on a ‘new scientific technique’ requires proof of its reliability—i.e., that the technique is ‘ “sufficiently established to have gained general acceptance in the particular field to which it belongs.” ’