Investigators say a 47-year-old Utah man accused of wanting to kill police officers and blow up a police department kept detailed logs of law enforcement activity.
FBI agents and Tremonton police arrested John Huggins on Thursday on a charge of possessing an unregistered destructive device.
Tremonton Police Chief David Nance says during an unrelated search of Huggins' trailer home in 2013, authorities found five spiral notebooks listing police activities and officer call signs.
Nance says the discovery caught officers' attention but police were not monitoring Huggins closely until a concerned citizen reported in February that he had been manufacturing explosives.
Authorities say he could face more charges as their investigation continues.
Huggins is being held until a detention hearing Tuesday afternoon.
It was not clear Monday whether he had an attorney.