The Bucks County man arrested Thursday for possessing three pipe bombs told Warrington Township police the explosive device he left in his mother's kitchen was intended for Fourth of July fireworks, but a federal investigator alleged in court papers Friday that if detonated, the device could have been deadly.

"From my training and experience, I know that fireworks are typically housed in paper tubing, which will not cause dangerous shrapnel to be created when lit," Agent Derek K. Valgora of the federal Bureau of Alcohol, Tobacco, Firearms and Explosives said in an affidavit filed in U.S. District Court in Philadelphia.

"These devices were housed in rigid PVC pipe, which would shatter and send high-velocity shrapnel in every direction upon explosion."

Valgora's statement was attached to a federal complaint accusing John Grzyminski, 50, of Saddle Drive in Warrington, of illegally possessing three pipe bombs, which are considered "destructive devices." It is unlawful for a person to possess such devices.

Grzyminski, who was living with his mother in Warrington, was also accused by local authorities of risking a catastrophe, and the illicit manufacture and possession of weapons of mass destruction.

He was taken into custody without incident Thursday after a Solebury Township patrolman spotted him driving his black pickup truck. Police quickly ruled out Grzyminski as a terrorist.

Papers filed Friday paint a portrait of an elderly, ailing mother named Catherine Wilson returning home after a hospital stay for surgery to a rude welcome — Grzyminski had removed her wheelchair access ramp to the house.

A short time later, Wilson and another son, Michael Grzyminski, entered the home and found something on the kitchen counter "resembling a large dog bone," Valgora testified in the affidavit.

Michael recognized the object with a "barbecue-type lighter beside it" as a pipe bomb and called police.

The device was several inches long, covered with white PVC pipe, and capped on both ends. Protruding from one end was a short piece of green "hobby-type fuse," Valgora wrote.

John Grzyminski left the scene after telling police the device was fireworks for Independence Day.

A police search turned up two similar pipebombs in a spare bedroom upstairs. The three devices were confiscated and detonated safely, according to the affidavit. Fragments were sent to the ATF Laboratory in Beltsville, Md.

Valgora said he found a black powder substitute called Pyrodex — an explosive propellant — as well as sections of PVC pipe, fuses, and tools used for drilling, on a workbench in the garage. He testified that all three devices were functional.

The bomb ingredients will be evaluated at an ATF laboratory, Valgora said.

Contact Bonnie L. Cook at 610-313-8232 or bcook@phillynews.com. Read her blog, "MontCo Memo," at www.philly.com.