The complaint said Gregerson earlier purchased "an arsenal of weapons, ammunition, tactical gear and tactical training materials." It doesn't say whether Gregerson was planning an attack or why he was purchasing explosives. The U.S. attorney's office in Detroit hasn't elaborated.
In June, the FBI said Gregerson bought road spikes online that can be used to slow or disable vehicles.
Other purchases included tactical training items, including handguns and dummy rounds.
"The purchase of training versions of these weapons makes it unlikely that the weapons were purchased for recreational use, such as hunting," the complaint states.