New Hanover County Jail Wilmington, N.C., police said Thursday they still didn't know why more than 20 explosive devices were hidden in Erik Rudolph Arnebold's home.

A North Carolina man was ordered held on $1.5 million bond Thursday after authorities discovered 24 bombs at his barricaded, security-camera-guarded home.

Erik Rudolph Arnebold, 37, was arrested Wednesday outside his home in Wilmington, N.C., and charged with multiple counts of possession of a weapon of mass destruction and single counts of possession of methamphetamine and possession of drug paraphernalia, according to court documents.

Bond, which was originally set at $625,000 when Arnebold was arrested, was more than doubled to $1.5 million during his initial appearance Thursday in New Hanover County District Court.

Police said they still didn't know why Arnebold had the arsenal of weapons — which, along with the bombs, also included a handgun, a rifle and an "extensive" collection of ammunition.

Wilmington police were initially interested in Arnebold as part of a simple drug investigation, police Capt. Jeff Allsbrook said in a statement. During that investigation, narcotics detectives developed information that Arnebold might be involved in making explosive devices, he said.

After consulting with the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives, they obtained a search warrant and called in the bomb squad, Allsbrook said.

When they arrived Wednesday, police and ATF agents found an explosive device "in plain sight" outside the home, which Allsbrook described as "constructed much like a fortress with windows and doors barricaded." Security cameras were also mounted outside.

Twenty-three other explosive devices were found behind a trap door under the floor, Allsbrook said. He wouldn't detail what kind of devices they were but said at least 12 of them contained lead shot, presumably to serve as shrapnel.

"The motive for the creation of all the devices remains under investigation," Allsbrook said. "However, through the work of law enforcement in Wilmington, we feel that any violent acts planned for the future were certainly thwarted."

Arnebold's next court appearance was scheduled for Nov. 21. He did not have an attorney who could be called for comment.

Watch US News crime videos on NBCNews.com