BUTLER, Pa.—A western Pennsylvania judge has rejected a defense motion to keep jurors from hearing about a weapon and other evidence found in the New Jersey home of a man slated for trial next month in the murders of his father and stepmother.

Forty-two-year-old Colin Abbott is charged in Butler County in the murders 65-year-old Kenneth Abbott and 55-year-old Celeste Abbott, whose dismembered remains were found in July 2011. Prosecutors, who are seeking the death penalty, allege that he told relatives that the two had died in a car crash.

Defense attorney Wendy Williams said the gun found in Abbott's Rutherford, N.J., home had three bullets, but police later noted only two. Judge William Shaffer said any discrepancy would "go to the weight of the evidence and not to its admissibility."