Police arrested 17-year-old John La Due Tuesday and charged him in juvenile court Thursday with four counts of attempted first-degree murder, six counts of possessing explosive or incendiary devices and two counts of criminal damage to property.
The charges say he told police he intended to kill "as many students as he could."
La Due now sits in a juvenile detention center.
"During his interview with officers, La Due revealed his plan was to kill his family members, start a diversionary fire in rural Waseca to distract first responders, and travel to the Waseca Junior/Senior High School," said Captain Kris Markeson of the Waseca Police Department.
Authorities say La Due planned to detonate the prepared bombs at the school. The devices were allegedly manufactured in a storage locker at a facility where the teen was taken into custody Tuesday night after a citizen saw him walk inside the unit and close the door.
"Officers observed materials in the storage locker which were consistent with bomb-making," said Markeson, "including a pressure cooker, pyrotechnic chemicals, steel ball bearings, and gun powder."
At his home, police found a 180-page notebook. The motive behind the plot remains unclear. But the plan laid out in the notebook detailed an attack police say John La Due didn't expect to survive.
"The members of the Waseca Public Schools community are deeply saddened and disturbed at the arrest of one of our students," said School Superintendent Tom Lee. "The information has been revealed in the case that we have escaped what could have been a horrific experience."
Lee said the 11th-grader was known to school officials but they had no major issues with him. He said teachers tried to reach out to him, but he was shy.
Markeson told reporters he could not divulge if specific students were targeted in the plot.
"This case is a classic example of citizens doing the right thing in calling the police when things seem out of place. By doing the right thing, (an) unimaginable tragedy has been prevented," Markeson said.
The investigation began in late March after three small explosive devices were discovered at an elementary school playground in the city of 9,400 people, about 80 miles south of Minneapolis. The youth allegedly admitted setting off practice bombs there.
According to the charging documents, The Free Press of Mankato reported, La Due allegedly told police he planned to shoot his mother, father and sister, then start a fire in a rural field to distract first-responders while he went to the school to set off pressure-cooker bombs in the cafeteria.
He also allegedly planned to throw Molotov cocktails, gun down students and kill a school liaison officer while he helped injured students.
He said his ultimate goal was for a SWAT team to kill him.
The teen allegedly referenced the Columbine, Virginia Tech and Sandy Hook school shootings in his notebook, and idolized the Columbine shooters.
The 17-year-old made his first court appearance Thursday and was sent to a juvenile detention center in Red Wing, the Star Tribune of Minneapolis reported.
His next court date is May 12.
The Associated Press contributed to this report.