A 13-year-old Vadnais Heights boy suspected of threatening to shoot up his middle school has autism and was simply repeating things he’d heard on the satirical cartoon “South Park,” his grandfather said Saturday.

The boy and his parents remained jailed Saturday, awaiting possible charges after authorities seized a cache of firearms, ammunition and at least one explosive device from their split-level home.

Ramsey County Sheriff Jack Serier said Friday that deputies were investigating a report that the boy threatened a classmate at the Academy for Sciences and Agriculture’s Maplewood campus. Officers with a search warrant later entered his Desoto Street house and found the weapons, some of which were unsecured, and other materials, including a ballistic vest.

Christopher Stowe, 41, and Lisa Stowe, 40, are being held on suspicion of negligent storage of firearms, a gross misdemeanor. Christopher also may face a felony weapons charge, and Lisa one count of obstructing the legal process, jail officials said Saturday. The boy was arrested on suspicion of making terroristic threats and is at the Ramsey County juvenile detention center.

“We had a potential tragedy averted from our community today,” Serier said Friday.

But the child’s grandfather, Mark Stowe, said the incident has been “blown out of proportion.” He said the teen made an empty threat on Wednesday with no plans to carry it out.

In the wake of the recent shooting in Parkland, Fla., that killed 17 people, students had begun speculating about possible attacks at their own school, the grandfather said. The 13-year-old had not been allowed to watch news coverage of the event, but wanted to sound tough and fit in.

“One of the older kids looks at [my grandson] and says, ‘What would you do? Would you bring a gun to school?’ ” Stowe recounted. “So he answers, ‘No, I wouldn’t bring a gun to school, I’d just shoot it up.’ ”

His remark got back to the principal, who issued a two-day suspension, Stowe said. A concerned parent later called police.

Mark Stowe was adamant that the guns in his son’s home are legal — mostly fourth-generation heirlooms from his family’s long military history. He assumes police were taken aback by the size of the collection. But Stowe said his family members are proud NRA members, concealed-carry-certified and all-around “good Christians.” Chris Stowe is a journeyman plumber, while Lisa Stowe handles logistics for a trucking firm.

“They’re law-abiding, private citizens,” said Stowe, who accused authorities of a “knee-jerk reaction.”

“Their rights have been absolutely trampled,” he said.

Residents of the quiet Vadnais Heights neighborhood said the Stowes have lived in the house for at least a decade, and also have an older teenage daughter. They described Chris Stowe as a handy guy who helped clear tree limbs and change flat tires. Lisa Stowe and their daughter often played softball outside.

Amid heightened security concerns at schools, educators have sought to reassure parents that their children are safe.

“This is a stressful situation, students may be experiencing anxiety and a sense of personal risk,” wrote Becky Meyer, the Academy for Sciences and Agriculture’s executive director. “We encourage parents to talk to their children about fear and violence.”

On Saturday night, Meyer sent another email explaining that privacy laws limited the details district officials could release. She apologized that many parents had to learn about the case through the media and assured them there is no outstanding threat to students.

"We are all part of the solution, and we hope you will work with us to help keep our children safe," she said.

Last week, Orono High School was placed on lockdown after threats of gun violence were posted on social media. A boy with autism was arrested at school but not charged. Community members raised more than $19,000 to help the family with legal and medical expenses.

Staff writers Chao Xiong and Miguel Otárola contributed to this report.