A short, unfinished note left by a 14-year-old boy contains no motive for why he shot and killed his mother and step-sister before committing suicide, the Grant County sheriff said Monday.

Detectives found the note, the contents of which have not been made public, in a search of the house where Aaron Harmon killed his mother and stepsister before killing himself Friday, Sheriff Bill Wiester said.

“There was no motive in this unfinished note,” Weister said in a statement released Monday. “The only indication was he had something that was troubling him.”

Harmon was a cousin of Arnold Fritz, 14, who was among three people fatally shot, allegedly by another student, in a Moses Lake junior high school classroom last February.

Autopsies conducted over the weekend concluded two weapons were used in Friday’s homicides and suicide, Wiester said.

Harmon’s mother, Linda Moore, 43, and stepsister, 9-year-old Mallory Moore, were shot in the head with a small-caliber rifle. Harmon used a large-caliber rifle to kill himself, the autopsy concluded.