The informant who is spurring the search for Jimmy Hoffa’s remains is an ailing prison inmate who recently passed a polygraph exam in the probe, says a government investigator who is familiar with the FBI operation in Michigan. The informant, Donovan Wells, 75, remembers “suspicious activity” on what is now called Hidden Dreams Farm in Milford Township, Mich., at the time Hoffa disappeared, the investigator said Friday. The investigator spoke on condition of anonymity because some of the information he was relating comes from records that have been ordered sealed by a federal judge. Among them is an FBI affidavit...