A device made of materials like those used in the 1995 Oklahoma City bombing could have been a former student’s “dry run” to see how authorities would respond to a bomb threat at Trident Technical College, Sheriff Al Cannon said Friday.

Local investigators and federal terrorism experts wouldn’t say whether the device could have exploded and caused damage near the North Charleston campus’ Student Center, which was mostly abandoned Monday for the holiday break.

The device contained ammonium nitrate, the same, readily available fertilizer that Timothy McVeigh used in his attack on the Oklahoma City federal building that killed 168 people.

An ignition device was attached to the package that included shrapnel — bits of steel and nails — and was wrapped in a plastic bag, the sheriff said.

Campus police fielded the threat via an email sent to a general school account. Investigators said they traced the message, as well as objects found in the explosive device, to 35-year-old William Gregory McGrath of North Charleston, a former student, who was arrested Thursday.

Investigators were trying to determine whether it was an effort to identify how authorities would respond to such a call.

“I don’t know if Trident Tech itself was the motive,” Cannon said. “(The intent) is very convoluted and confusing. ... It obviously had the school concerned” and was important “in light of the events in Connecticut.”

Deputies, officers and agents on Thursday searched McGrath’s home and a nearby storage shed at the Alta Shores apartments at 2605 Elms Plantation Blvd.

In the shed, they found commercial fireworks and traces of ammonium nitrate, according to arrest affidavits. Eight live marijuana plants also were unearthed in the master-bedroom closet of McGrath’s apartment, the documents stated.

It’s not known whether the fertilizer was used to cultivate the plants. The operation also included seeds, lighting, a fan and cups of soil.

McGrath faces charges of manufacturing, possessing and placing a destructive device, as well as growing marijuana. Both are felonies. The bomb count is punishable by 25 years to life in prison.

Mount Pleasant police officers have arrested McGrath twice, according to the State Law Enforcement Division, on charges of driving under the influence in 2007 and malicious injury to personal property in 2009.

During a bond hearing Friday, McGrath told Magistrate Linda Lombard that he supported himself with an E-commerce business that he ran out of his home.

Lombard set his bail at $100,000 on the explosives charge and $25,000 on the marijuana count. No one else spoke in his favor during the proceeding.

“I have no idea what this fake bomb charge is about,” he said. “I really need an attorney. I’ve never been in trouble before.”

The sheriff said a collaborative effort between local and federal agencies will follow up on remaining questions.

Federal investigators who are assisting think that McGrath acted alone and that no other schools are in danger, Cannon said.

McGrath once attended Trident Tech, though it wasn’t immediately known what he studied or whether he completed a degree, campus Police Chief Larry Savidge said.

The email allegedly sent by McGrath indicated where an explosive device had been placed on the Rivers Avenue campus. Savidge found the object before 4 p.m. Monday in some bushes near the school’s Student Center.

Using a robot, technicians from the Charleston County Sheriff’s Office bomb squad unwrapped the bag around the device and defused it.

“By and large,” the sheriff said, it was not a heavily traveled spot.

“The school had been shut down for the winter,” Savidge added. “But we have a heightened sense of security all the time.”

Prentiss Findlay contributed to this report.