Robert Lee Yates Jr.
Firearm examination evidence from the cases of Nickie Lowe and Kathy Brisbois, conducted by Gaylan Warren of the Columbia International Forensic Laboratory, showed that those two cases were without question related. It was Warren's opinion that the same-.22-caliber weapon, most likely a handgun, killed Lowe and Brisbois. Warren further determined that Sherry Palmer had been shot with a .32-caliber firearm which, in his opinion, was most likely a semi-automatic pistol.
The Washington State Patrol Crime Lab examined ballistics evidence in the case of Patricia Barnes, and the .22-caliber bullets found in her body had been too badly damaged from passing through tissue and bone and had been rendered useless for comparisons under a microscope. Although it was possible, even likely, that the bullets had been fired from the same gun that was used to kill Lowe, Joseph, and Brisbois, their uselessness made it impossible to conclusively make that determination.
Similarly, the firearms evidence in the Zielinski case, as well as several of the other cases, was deemed inadequate for comparison with other bullets and bullet fragments recovered from the other victims. Although forensic scientist Ed Robinson of the Washington State Patrol Crime Laboratory determined that Zielinski had been shot with a .25-caliber weapon, most likely a semi-automatic pistol, he was unable to determine whether any of the other victims that had been shot with a .25-caliber weapon had been shot with the same gun. Robinson was able to determine that Magtech, a brand that had limited availability within the state, manufactured the bullets recovered from Zielinski's body.
The firearms evidence in the Hernandez, Wason, Maybin, Johnson, McClenahan, Oster, and Ellis cases showed that the victims had been shot with a .25-caliber weapon, most likely a semi-automatic pistol. Ballistics comparisons of the bullets from each of those cases showed that all of the bullets had been fired from the same gun, with the exception of the bullets recovered from the bodies of Hernandez and Ellis. The bullets recovered from Hernandez' and Ellis' bodies had similar characteristics as the bullets recovered from the other aforementioned cases, but they could not be linked conclusively as having been fired from the same gun. It was pointed out to the investigators that the ammunition used in the Hernandez case was identified as Magtech brand, the same brand of bullet that was used to kill Zielinski, but the bullets used in the Ellis case was of a different brand, similar to Remington or Winchester.
The firearms evidence in the Mercer case was compared with the evidence from the other cases. The bullets were determined to be Magtech brand again, and it was determined that the bullets that killed Mercer were fired from the same gun that killed several of the other victims. The firearms evidence in the Derning murder included a .25-caliber CCI brand cartridge case that matched general characteristics of those found in the Mercer case, indicating that Mercer and Derning had been killed by bullets fired from the same gun. However, the evidence linking those two cases only bore similarities, and it was not conclusively shown that bullets fired from the same gun had in fact killed both women.