"They did their investigation, they didn't find enough probable cause and they didn't bring an indictment," Arpaio said at a hastily called news conference after returning from the Republican National Convention in Florida. "We don't go around framing anybody. My people are not crooks."
Assistant U.S. Attorney Ann Birmingham Scheel released a statement saying her office "is closing its investigation into allegations of criminal conduct" by current and former members of the sheriff's and county attorney's offices.
Scheel, who is based in Arizona, said she was acting on behalf of the U.S. Department of Justice. In a four-page letter to Maricopa County Attorney Bill Montgomery explaining the decision, Scheel wrote that "our limited role is to determine whether criminal charges are supportable. After careful review, we do not believe the allegations presented to us are prosecutable as crimes."
"I've been in law enforcement for 50 years. Nothing surprises me. But I know my people did the right thing," said the 80-year-old Arpaio, who is running for a sixth term as sheriff in Arizona's most populous county. "I'm just happy for my organization, for my deputies. Not for me."
The federal probe focused specifically on the sheriff's anti-public-corruption squad. In a separate probe, the U.S. Justice Department has accused Arpaio's office of a wide range of civil rights violations, and in another case, a federal judge has yet to rule in a civil case brought by a group of Latino plaintiffs that claimed Arpaio and his deputies engaged in racial profiling.
The timing of the federal authorities' announcement at 5 p.m. on a Friday before a holiday weekend was questioned by some Arpaio critics.
"It is a miscarriage of justice that the federal government is dropping its case against Sheriff Arpaio and to make such an announcement on the Friday night before the Democratic National Convention can only be politically motivated to shield the administration from criticism," Pablo Alvarado, director of the National Day Laborer Organizing Network, said in a statement.
Arpaio and his top ally, former County Attorney Andrew Thomas, were embroiled in a three-year feud with county officials and judges and defended their investigations as necessary to root out corruption.
The officials who were targets of the investigations contend the probes were trumped up as retaliation for political and legal disagreements with the sheriff and prosecutor.
Criminal cases against former Superior Court Judge Gary Donahoe and county supervisors Mary Rose Wilcox and Don Stapley were dismissed after a judge ruled that Thomas prosecuted one of the three officials for political gain and had a conflict of interest in pressing the case.
Authorities say the charges against Donahoe were filed in a bid to prevent the judge from holding a hearing regarding Arpaio and Thomas' claim that judges and county officials conspired to hinder a probe into the construction of a court building.
Donahoe had disqualified Thomas from handling the court building investigation and was poised to hold another hearing over a request to appoint special prosecutors to handle the probe. The hearing was called off after the charges were filed against the judge.
The judge also had been critical of the ability of Arpaio's office to bring inmates to court on time for hearings.
Thomas was disbarred in early April by an ethics panel of the Arizona courts that found he brought unsuccessful criminal cases against the judge and two county officials for the purpose of embarrassing them.
In the separate probe, which is still ongoing, the Justice Department says Arpaio's office racially profiles Latinos, retaliates against critics of its immigration patrols and bases its immigration patrols on racially charged citizen complaints that did not allege crimes. The sheriff denies the allegations.
And in the civil case, the Latino plaintiffs aren't seeking monetary damages. Instead, they want a declaration that Arpaio's office uses racial profiling and an order requiring policy changes. If Arpaio loses the case, he won't face jail time or fines.