El Mirage Detective Jerry Laird, who reviewed some the investigations, learned from a sheriff's summary of 50 to 75 cases files he picked up from Arpaio's office that an overwhelming majority of them hadn't been worked.

Arpaio's office was under contract to provide police services in El Mirage as the city struggled with its then dysfunctional department. After the contract ended and El Mirage was re-establishing its own police operation, the city spent a year sifting through layers of disturbingly incomplete casework.

Sands said officers had subsequently moved to clear up inadequately investigated sex-crimes in El Mirage and elsewhere in the county. He said leads were worked if they existed and cases were closed if there was no further evidence to pursue.

Brian Sands, a top sheriff's official who is in charge of the potential discipline of any responsible employees, was later made available to talk about the cases. He declined to say why they weren't investigated. "There are policy violations that have occurred here," Sands said. "It's obvious, but I can't comment on who or what."

Arpaio's office refused several requests over a period of months to answer questions about the investigations and declined a public records request for an internal affairs report, citing potential disciplinary actions.

The botched sex-crimes investigations have served as an embarrassment to a department whose sheriff is the self-described "America's Toughest Sheriff" and a national hero to conservatives on the immigration issue.

Many of the victims, said a retired El Mirage police official who reviewed the files, were children of illegal immigrants.

In El Mirage alone, where Arpaio's office was providing contract police services, officials discovered at least 32 reported child molestations -- with victims as young as 2 years old -- where the sheriff's office failed to follow through, even though suspects were known in all but six cases.

Both cases were among more than 400 sex-crimes reported to Maricopa County Sheriff Joe Arpaio's office during a three-year period ending in 2007 -- including dozens of alleged child molestations -- that were inadequately investigated and in some instances were not worked at all, according to current and former police officers familiar with the cases.

Seven months before, in an apartment two miles away, another 13-year-old girl was fondled in the middle of the night by her mother's live-in boyfriend. She woke up in her room at least twice a week to find him standing over her, claiming to be looking for her mother's cell phone.

EL MIRAGE, Ariz.—The 13-year-old girl opened the door of her home in this small city on the edge of Phoenix to encounter a man who said that his car had broken down and he needed to use the phone. Once inside, the man pummeled the teen from behind, knocking her unconscious and sexually assaulting her.

That meant there were no follow-up reports, no collection of additional forensic evidence and zero effort made after the initial report of the crime was taken.

"I think that at some point prior to the contract (for police services) running out, they put their feet on the desk, and that was that," Laird said.

Arpaio acknowledged his office had completed an internal probe into the inadequate investigations, but said, "I don't think it's right to get into it until we get to the bottom of this and see if there's disciplinary action against any employees."

A small number of cases from El Mirage were handed over to prosecutors, but the El Mirage Police Department said most were no longer viable -- evidence dating as far back as 2006 had grown cold or wasn't collected in the first place, victims had either moved away or otherwise moved on.

Bill Louis, then-assistant El Mirage police chief who reviewed the files after the sheriff's contract ended, believes the decision to ignore the cases was made deliberately by supervisors in Arpaio's office -- and not by individual investigators.

"I know the investigators. I just cannot believe they would wholesale discount these cases. No way," Louis said. "The direction had to come (from) up the food chain."

Louis said he believes whoever made the decision knew that illegal immigrants -- who are often transient and fear the police -- were unlikely to complain about the quality of investigations. He said some cases also involved families here legally.

El Mirage paid the sheriff's office $2.7 million for a wide range of police protection from 2005 through mid-October 2007, after the city's police department had been criticized in an audit as poorly organized, loosely supervised and mismanaged.

Although a small number of El Mirage officers continued working there during the period, Arpaio brought in patrol officers and detectives and managers who ran the department.

El Mirage police files obtained by The Associated Press through public records requests establish a pattern of sex-crimes not actually being investigated after the crimes were reported to Arpaio's office.

In April 2007, a 3-year-old girl was reported molested by her father, an illegal immigrant who cared for the child while her mother was at work. When the mother confronted her husband about the abuse, he cried and swore he'd never do it again.

Yet a few days later, the mother noticed more signs of sexual abuse on her daughter and called for help. After the initial report, that help didn't come.