Schallenberger, 18, was not badly injured, but his parents also called a local mental health clinic that offered no help, Hodge said. A spokesman for the clinic would not confirm or deny any contact with the family, citing state law.
Hodge said he plans to ask that Schallenberger undergo a mental evaluation at the teenager's bail hearing Tuesday.
Schallenberger was arrested after his parents called police because he had ordered 10 pounds of ammonium nitrate, an explosive commonly used as fertilizer and was employed in the deadly 1995 Oklahoma City bombing.
Authorities checked the school for bombs over the weekend and on Monday students walked through newly installed metal detectors and past law officers. Still, officials said 60 percent of the school's 544 students stayed home.
The quiet teenager with a slight build and a wispy mustache had apparently been planning the potentially deadly attack for months, authorities said.
"This kid had the intellect and the means and the materials to carry it out," Hodge said.
Police said they discovered a hate-filled journal lauding the Columbine killers, an audiotape to be played after he perished during his rampage and a year's worth of plans for the bombing that included a hand-drawn map of the school.
"He's just a soft-spoken little kid," Hodge said, adding that Schallenberger threatened to something "very violent."
Schallenberger was charged with making a bomb threat and will be charged Tuesday with possession of bomb-making material, Hodge said. He was assigned a lawyer, William Spencer, who did not return calls from The Associated Press.
During a brief court hearing Monday, the teen was silent but appeared agitated - his eyes widening at the sight of cameras awaiting him when he entered in an orange jumpsuit, hands cuffed and ankles shackled.
Schallenberger's mother and stepfather, John and Laurie Sittley, could not be reached for comment.
Their phone number was unlisted, they did not attend the hearing, and their home about 10 miles from the school was blocked by "No Trespassing" signs. Authorities said Schallenberger has eight siblings and step-siblings.
Sheriff Sam Parker said the teenager's "heartbroken" parents deserved praise for calling authorities when they retrieved the ammonium nitrate from a post office after receiving a delivery notice at home.
"Without the parents, Chesterfield County would've suffered. We thank them," Parker said.
Authorities said Schallenberger's journal did not specify targets of an attack, or a date that he planned to carry it out. Randall Lear, the town's police chief, said Schallenberger was "just mad at the world."
The Columbine attack happened nine years ago Sunday, but Lear said investigators do not know whether there was any link between the anniversary and Schallenberger's plans.
Hodge said the teen was set to graduate this year and had no history of bad behavior. Schallenberger was on the school's academic bowl squad and had won an award from a local college a year earlier.
Students said the teen often ate alone in the cafeteria and were surprised at the accusation.
"I never though he'd be the dude to do something like this," said James Ford, a 16-year-old sophomore.
Some adults who had met the teen said the accusations were surprising.
"He wouldn't hurt a flea," said neighbor Carl Parker, who described Schallenberger as well-mannered and a sports fan who used to watch a neighbor's pets when he was younger. "People just don't know him like I do. He's a good kid."
The sheriff said Schallenberger bought the ammonium nitrate off eBay. A spokeswoman for the Internet auction site, Nichola Sharpe, said the substance is legal to sell though it must be specially shipped.
Sharpe said eBay's fraud investigation unit was working with law enforcement on the case.
Chesterfield is a town of about 1,500 people in northeastern South Carolina near the North Carolina line.
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Associated Press writers Jim Davenport and Katrina A. Goggins in
Columbia and Bruce Smith in Charleston contributed to this report.
