FBI agents investigating Maricopa County, Ariz., Sheriff Joe Arpaio, former County Attorney Andrew Thomas and their top deputies on abuse-of-power allegations believed they had sufficient evidence to charge some of the probe’s targets, The Arizona Republic reported.

Federal prosecutors ultimately declined to pursue the case, citing “a lack of evidence or an insurmountable burden of proof,” the newspaper said.

The blustery Arpaio – known nationally for publicity-garnering stunts such as requiring inmates to wear pink underwear, reinstituting chain gangs and setting up “Tent City,” an extension of the county jail that Arpaio called a “concentration camp” – has accused U.S. officials of engaging in a politically motivated witch hunt.

The three-year investigation concluded in August 2012, when the U.S. Attorney’s Office for Arizona announced there would be no indictments. The investigation’s targets were scrutinized for civil-rights violations, misuse of public money and perjury, according to the paper.

Within days, the Republic submitted a Freedom of Information Act request for the prosecutor reports. This week, the Department of Justice delivered 93 pages, two-thirds of them blacked out completely, citing privacy rights, according to the newspaper.