A fifth grade boy in Washington state was found guilty on Friday of conspiracy to kill one of his classmates, following a trial the presiding judge declared as “the most serious of my career."

The boy (whose name is withheld because of child privacy laws) conspired with a 10-year-old classmate to stab a female classmate to death at Fort Colville Elementary School in northeast Washington last February. The boys were caught with a handgun and a knife when they tried to enter school that day.

The defense attorneys for the boy attempted to portray the child as unable to distinguish between fact and fiction. The judge however, found that “simple anger” had driven the plot, and the boys were fully aware of what they were doing.

After being caught, the boys admitted to a school counselor that one of them would stab the girl to death because she was “really annoying," while the other would point the gun at anyone who tried to stop them.

The younger boy has already plead guilty and was sentenced to three to five years in juvenile detention. The sentencing for the older boy will be in November.

“There is no joy in a conviction,” the county prosecutor, Tim Rasmussen, told reporters.