WASECA, Minn. (AP) — A judge has dismissed the most serious charges against a 17-year-old boy accused of plotting to kill his family and attack his southern Minnesota school.

KEYC-TV Waseca County Judge Gerald Wolf on Monday dismissed four counts of attempted murder and two counts of attempted damage to property.

In his ruling, Wolf said prosecutors failed to show sufficient evidence that the boy had moved beyond the preparation stage to substantial preparation needed to support the charges.

The judge allowed six counts of possession of explosives to stand.

The teen was arrested in April after authorities said they found him in a storage locker with bomb-making materials.

Prosecutors want to certify the teen to stand trial as an adult.