Joe Arpaio investigates his political opponents and brings false charges against them–that much we know. Whether those actions are crimes has not been proven, nor will it be now that the Justice Department has closed its lengthy criminal investigation of Arpaio. For more on that story, you can read about it at US News and World Report.
While we don’t have inside information on the criminal investigation, it is almost certain that same allegations that led to the disbarment of former Maricopa’s County Attorney, Andrew Thomas are involved here. Arpaio is not out of the woods yet. There is a large ongoing consolidated federal civil lawsuit against Arpaio and others on behalf of individuals alleging that they were unjustly targeted in bogus politically-motivated criminal investigations by Maricopa County law enforcement and Joe Arpaio in particular.
The criminal investigation is not to be confused with the federal civil lawsuit against Arpaio and the Maricopa County Sheriff’s Office, which is ongoing. That lawsuit alleges racial profiling and mistreatment of minority prisoners.