He told agents he ordered large quantities of "black powder" online and built small test explosives before constructing the 200-pound explosive device in a plywood box in his basement. He said he installed certain components in the device to ensure that he was killed in the blast.
On Wednesday, FBI technicians removed the bomb from his basement and transferred it to a safe location.
At a Senate hearing Wednesday morning, FBI Director Christopher Wray said his agents are investigating about 1,000 homegrown terror threats in all 50 states.
"Those cover the waterfront of the full range of extremist ideologies from right to left and everything in between," Wray said.
Rosenfeld made his first appearance in New York federal court earlier Wednesday. The FBI says they do not believe he is part of any larger terrorist organization. He faces up to 20 years in prison if convicted.
