By Chuck Conder, CNN

Phoenix, Arizona (CNN) -- Maricopa County Sheriff Joe Arpaio calls himself "America's toughest sheriff." He is famous for creating a tent city jail in the Arizona desert; for providing pink underwear for inmates; for bragging that he spends more to feed his dog than a prisoner in his jail.

This year he has made national headlines for his tough enforcement of Arizona's anti-illegal immigration laws and for his vocal support for a controversial new immigration law that takes effect at the end of July.

But the 77-year-old lawman is himself the subject of serious allegations of abuse of power. Arpaio's critics say he has a long history of launching bogus criminal investigations against political opponents and anyone else who gets in his way.

This year a federal grand jury started looking into the allegations.

Former Maricopa County School Superintendent Sandra Dowling says what happened to her is a case in point.

Dowling says was locked in a political battle with some members of the Maricopa County Board of Supervisors over school district funds when the sheriff's SWAT team came in the dead of night to search her home. Dowling was charged with stealing money from a school for homeless students. There were 25 felony counts in all.

"Never could I have imagined what a nightmare was waiting ahead," Dowling said.

Arpaio promised to uncover massive public corruption -- "We are looking into all avenues of this investigation," he said -- and to win a speedy conviction.

From the start Dowling maintained her innocence: "I kept saying I didn't do anything. I didn't do anything."

It took three years, but finally a judge threw out all the felony counts against Dowling. She entered a guilty plea to a single misdemeanor charge. But she said her reputation had been shattered, her career destroyed, and she owed more than $100,000 in legal fees.

"I still don't think that everybody knows I was innocent," she said.

Dowling is not alone. Arpaio has launched -- either on his own or in conjunction with the county attorney -- high-profile criminal investigations against a who's who of Maricopa County politicians and officials. The list includes the mayor of Phoenix, a former police chief, two members of the board of supervisors, Superior Court judges, and even a former state attorney general.

The charges have included public corruption, misuse of taxpayers' dollars, bribery, rape and even child molestation. What all these investigations hold in common is that they were launched with great public fanfare, but rarely resulted in convictions. Among the investigations recounted in this report, the only conviction has been on the misdemeanor charge against Dowling.

Phoenix Mayor Phil Gordon calls the sheriff's long list of investigations a "reign of terror."

Gordon came under Arpaio's scrutiny, he says, after speaking out against the sheriff's neighborhood sweeps to round up illegal immigrants.

The mayor says he received a torrent of records requests from sheriff's investigators, and he was later told that he was under investigation on possible child molestation charges. Gordon says the sheriff "bragged that he was watching my office from his office with a telescope."

The sheriff's department confirmed that Gordon was investigated on child molestation accusations. In the end charges were never filed.

"He is a coward," said former Buckeye, Arizona, Police Chief Dan Saban. In 2004 Saban challenged Arpaio's bid for a fourth term in the sheriff's office. That was when the local news reported that Arpaio was investigating his rival on charges of rape.

It was a claim made by Sabin's foster mother. She claimed the rape occurred 30 years earlier, when Saban was only 15 years old. Saban says he was the victim, not the foster mother.

Once again charges were never filed. But Saban noted the sheriff alerted the media to the details of the sordid accusation. "They put out a media campaign against me," he said. "That I was the subject of a criminal probe."

It sounds familiar to County Supervisor Don Stapley. "They indicted me on 118 counts." he said, "none of which I'm guilty of."

Those 118 counts of public corruption against Stapley made big headlines before they were thrown out of court by a judge. Arpaio has refilled many of those charges and Stapley is still fighting to clear his name.

Arpaio turned down CNN requests for an interview, citing the federal grand jury investigation and a series of threatened lawsuits from these and other cases.

However, one of Arpaio's long-time assistants was eager to defend his boss.

Deputy Chief John MacIntyre says that in each and every case, the sheriff's investigations were fully justified. "Was there probable cause? There was a ton of probable cause," he said.

In the rape investigation of the sheriff's political rival, Saban, for example, MacIntyre says it was a case the sheriff had to investigate. "We didn't make up the mother's testimony," he said. "It came in here like a bombshell."

MacIntyre says it was just coincidence that the sheriff benefited when the story was leaked to the press.

Andrew Thomas is another Arpaio ally. He is the former Maricopa County attorney who participated in a number of Arpaio's high-profile cases. He is currently running for the Arizona attorney general's office.

He, too, defends Arpaio's investigations, saying, "The reality is these were legitimate cases that needed to be brought."

"It wasn't just brought up out of thin air, there was evidence to back up those cases," he said.

The sheriff's critics, he said, are "being portrayed as martyrs and I feel that's absolutely inaccurate."

Thomas paints a picture of Maricopa County as a pit of corruption that includes the judicial system, which he blames for his lack of convictions. "We had to go into courts where the judges were collaborating with the targets of the investigations," he said. "They were working together to thwart investigations (and) prosecutions."

The Arizona Bar Association takes a different view. Its ethics committee is currently considering a case against Thomas for his role in Arpaio's investigations of public officials, the association said.

MacIntyre says it is up to the public to untangle the web of political intrigue surrounding Phoenix and its environs. "The electorate is going to have to say we don't want to do this anymore, and we will vote one or more people out," he said. "Right now the sheriff's polls indicate that the public still supports him rather overwhelmingly."

Whether the grand jury investigation or the threatened lawsuits bring change remains to be seen.

Mike Lacey, a newspaper editor who was once arrested after criticizing Arpaio, says the end is not yet in sight: "If you are a critic of the sheriff, or if you represent an opportunity for publicity, you become a target for this man."