Josh Magee, 17, was also found with a note saying he wanted to injure everyone at the school except for three friends.
Magee was arrested Tuesday in the parking lot of Malcolm High School after a staff member saw him swigging liquor from a flask and putting on a black overcoat. He was charged Wednesday with attempted murder.
Police who searched Magee's car found a bolt-action rifle, several rounds of ammunition, small bottles of propane and rigged containers of a petroleum-based propellent.
"It had the potential of going badly," said Superintendent Gene Neddenriep. "With this student, at this school, on this particular day, we were successful. We got lucky."
Parents and school officials in this tiny town north of Lincoln said Magee often spoke about the, in which Eric Harris and Dylan Klebold killed 12 students and a teacher before killing themselves.
"He asked them in class last week if they knew who Eric Harris and Dylan Klebold were," said Julia Lostrah, whose daughter is Magee's classmate. "Then he said, `I know them."'
The arrest came in the same week that authorities in another rural town in the heartland averted a potentially violent school encounter.
Two second-grade boys and an 11-year-old schoolmate were arrested Wednesday in Forsyth, Mont., on charges that they buried a loaded handgun in a playground sandbox and plotted to shoot and stab a third-grade girl during recess. Authorities said the boys intended to harm the young girl because she had teased two of them.
No one answered the door Thursday at Magee's red-brick home just down the road from the school in Malcom, a town so small that its downtown streets are unpaved.
School and law enforcement officials said his mother works as a chef in Lincoln, and his father is serving in Afghanistan in the military.
Magee, who has attended Malcolm schools since kindergarten, has always been on the district's radar, Neddenriep said.
"All the way through, he was just a little different," he said. "He liked to be alone, he didn't take part in many things. His enjoyment was weapons."
The superintendent said he wasn't aware of reports that Magee was a target of bullies. "There were never any incidents reported," he said.
When students began reporting to faculty that Magee bragged of making and testing explosives at home, Neddenriep said, the school paid close attention to the teen.
Magee then began showing some interest in school activities, he said.
Lostrah, who is also the school district's administrative assistant, said Magee joined the cross-country team and was an impressive musician.
"He was very talented," she said.
Magee was being held in a juvenile jail, but he was charged as an adult with attempted first-degree murder.
Neddenriep said the school of about 450 students will refine its safety policies in the wake of Magee's arrest.
"There's one thing I did learn," Neddenriep said. "It can happen anywhere."