Investigators aren’t sure what a 13-year-old Walton County boy was planning to do with the two explosives he allegedly made at home. But they weren’t taking any chances, the county’s sheriff said Tuesday night.

The teenager, whose name was not released, was arrested Monday morning after the devices were found in his bedroom, Sheriff Joe Chapman said. Deputies were called to a home on Snows Mill Road, near Monroe, after the teen’s mother found something suspicious in his room, Chapman said.

“The mother had found a knife sewn in the lining of a jacket and it definitely alarmed her,” Chapman told The Atlanta Journal-Constitution.

While searching the boy’s bedroom, investigators found what appeared to be a pipe bomb, made from plastic pipe, Chapman said.

“We called the GBI’s bomb squad to come out to the home,” Chapman said.

Further search of the home led investigators to a hand grenade the teen also allegedly made.

“It was designed to go off on impact when thrown,” Chapman said.

The teenager was arrested and remained Tuesday night at a youth detention center, according to police. Investigators have not yet determined what the middle school student planned to do with the devices, Chapman said.

“Was he going to take them to school? We don’t know,” Chapman said.