The move put an end to an investigation that began in 2008 and included use of a federal grand jury. Multiple high-level Maricopa County sheriff's officials testified before the grand jury in 2010, but the probe went quiet in recent months.
The FBI led the investigation and was said to be looking at whether Arpaio used the powers of his office to target his political enemies. At one point in 2009, his office along with the county's elected prosecutor were investigating at least 14 local government officials, all of whom had defied Arpaio in some way. The targets included judges, politicians and others officials high up in local government.
The news release said federal authorities were dropping the case against current and former members of both the sheriff's office and the Maricopa County Attorney's Office.
The decision comes just three days after Arpaio, 80, won the Republican primary for sheriff, a race in which he was unopposed. First elected in 1992, he is seeking a sixth term in office this year and will face off against Democrat Paul Penzone and independent Mike Stauffer in November.
The decision also comes a few months after an arm of the Arizona Supreme Court said there was evidence "beyond a reasonable doubt" that Arpaio and some of his closest allies had committed a federal crime in December 2009 during his feud with local officials. The ruling prompted several former prosecutors to call on the Justice Department to either charge Arpaio with a crime or end the investigation altogether.
Among those prosecutors was a one who used to lead the same office that just cleared Arpaio, former U.S. Attorney Paul Charlton. In an interview with TPM in April, Charlton said he agreed with the panel's ruling and believed federal investigators had more than enough evidence to charge Arpaio and others with a crime.
"It's time for these guys to make a decision," Charlton said.
On Friday, federal prosecutors also sent a letter to at least one of the agencies that had been investigated. Addressed to the Maricopa County Attorney's Office, the letter focused largely on the part of case that involved that agency but it also touched on the sheriff's office. Arpaio's name appeared only once, but the prosecutors made it clear there were other aspects of the investigation that weren't being included in the letter. TPM got a copy of the letter through a public records request.
In it, federal prosecutor Ann Birmingham Scheel wrote that investigators looked into a number of issues, including alleged misuse of money by the sheriff's office and alleged prosecutorial misconduct by the former elected head of the office, Andrew Thomas, as well as others.
But in the end, Scheel wrote, there just wasn't enough evidence to meet the heavy burden it takes to bring criminal charges against fellow prosecutors and police who are given a lot of room to serve justice as they see fit.
"Law enforcement officials are rightfully afforded a wide swath of discretion in deciding how to conduct investigations and prosecutions," Scheel wrote. "Unfortunately, such discretion can act as a double-edged sword: although it empowers fair-minded prosecutors and investigators to discharge their duties effectively, it also affords potential for abuse. Our limited role is to determine whether criminal charges are supportable."
Scheel also said it was clear other people in the community felt strongly that abuses had taken place. However, those abuses didn't rise to the level of crimes in her view.
"If there is one lesson to be drawn from the arrests, investigations and lawsuits of the past few years, it is that prosecutors, in seeking justice, must exercise their charging discretion with great care," she wrote, adding: "But criminal prosecutions have the highest standard of proof. Based on our careful review of the facts and the law, we have decided to decline prosecution in these matters."
Meanwhile, the Justice Department's civil case against Arpaio continues. Earlier this year, the department's Civil Rights Division sued the sheriff and his agency, alleging widespread abuse and profiling of Latinos. A department spokesperson told TPM late Friday that case was still ongoing.
Additional reporting by Ryan J. Reilly.