TOPEKA, Kan. (AP) — Newly released court records say a Topeka car explosion that severely injured a 4-year-old boy also peeled back the vehicle’s metal roof.

The Topeka Capital-Journal  reports that it obtained an affidavit Tuesday in the case against Jacob Daniel Schell. The 37-year-old was charged earlier this month in the July 5 explosion.

The affidavit says that a sack containing “several improvised explosive devices” blew up in the lap of Schell’s son. A Kansas Highway Patrol trooper said the ignition source was a “little cap gun” the boy was using.

Schell described what exploded as leftover fireworks from a campout. But the state fire marshal’s agent said damage to this vehicle was consistent with commercially made or homemade explosives. Schell’s attorney didn’t immediately return a phone call from The Associated Press.