A Detroit man accused of amassing weapons and buying explosives from an undercover agent will remain in jail while his case is in court, despite his lawyer's claim that he's just a survivalist.

Defense attorney David Tholen says the government is exaggerating the threat of Sebastian Gregerson. But federal Magistrate Mona Majzoub wondered Thursday why Gregerson would have certain items typically used for "death and destruction."

The 29-year-old Gregerson is charged with possessing an unregistered destructive device. The FBI said he was arrested Sunday in Monroe after buying grenades from an undercover agent.

Prosecutor Cathleen Corken told the judge that Gregerson appeared to be preparing for violent acts. She called him a dangerous man.