A Minnesota 18-year-old accused of planning to kill his family and attack his high school will stand trial as an adult on explosives charges, a judge ruled Friday, citing the seriousness of the allegations.

Waseca County District Judge Robert Birnbaum also ordered that John LaDue be immediately transferred from a juvenile center to the county jail pending his first adult court appearance.

Defense attorney Dawn Johnson said they're disappointed and considering whether to appeal.

LaDue is 18 now but he was 17 when he was arrested in April 2014 after police found him in a storage unit with bomb-making materials. Authorities also seized firearms and ammunition from his home.

Court records say he told investigators he planned to first kill his family members, then go to Waseca Junior/Senior High School, kill the school's police liaison officer, then kill as many of his fellow students as possible by setting off bombs and shooting them in the ensuring confusion.

He directed police to an extensive handwritten journal detailing his plans and admitted setting off incendiary devices around Waseca. At first he said it was a way to practice for the attack and see if he could outwit law enforcement, but later changed his story to say he set off the devices to relieve pressure.

A different judge dismissed attempted-murder charges for lack of probable cause last year, but LaDue still faces six counts of possessing explosive devices.

In his findings of fact, Birnbaum noted expert testimony from a hearing in June that LaDue has been diagnosed with autism spectrum disorder. He said LaDue showed deterioration in adolescence, becoming more isolated while his ability to deal with relationships and have empathy for other people deteriorated.

Birnbaum wrote that prosecutors established that the public safety would not be served by trying LaDue in the juvenile system, where could be kept no longer than his 21st birthday. He said that's not enough time for the treatment, rehabilitation and monitoring LaDue needs.

If LaDue is convicted as an adult on all six counts of possessing explosive devices, he would face a five-year sentence under the Minnesota Sentencing Guidelines, Waseca County Attorney Brenda Miller has said.