Often, one story leads to another. And that's just what happened in this case.

I got a call in April from a family in Biloxi, Mississippi, whose home had been destroyed by Hurricane Katrina. In 2006, I'd reported on their plight and the good Samaritan who rebuilt their home.

But this call was different. The family's only grandson, 21-year-old Lee Demond Smith, had died in December while being held on a parole violation in the Harrison County Jail in Gulfport, Mississippi. The county autopsy said his death was from natural causes, a "massive recent pulmonary embolism," a blood clot in the lungs.

The family, though, was reluctant to accept that finding. Lee had never before had any health problems. And they learned of his death by getting calls from the families of other inmates at the jail. The jail itself denied for hours that anything was wrong. Family members weren't allowed to see Lee's body until the day he was buried.

But most disturbing were the stories the family had long heard about inmates being beaten by guards. So the local community rallied around them, raising $9,000 to ship Lee's body to Nebraska for a second autopsy.

The Smith family contacted me after the results came back. Forensic pathologist Dr. Mathias Okoye found that Lee had been strangled. The precise cause of death was "asphyxia due to neck compression and physical restraint while in police custody." Okoye was particularly shocked to find Lee's lungs had never been dissected. Both Okoye and another forensic pathologist we interviewed agree that is the only way to confirm a blood clot in the lung as a cause of death.

Still, the county stands by its original autopsy, though it refused to release its autopsy photos to CNN. (Hear Smith's family talk about their suspicions)

We also traced the troubled history of the Harrison County Jail. Four prisoners have died due to unnatural circumstances there since 2002. One of them was beaten to death in February 2006 in front of cameras in the jail's booking room.

Four guards go on trial next month accused of his murder.

Since then, four more have pleaded guilty to abusing other inmates. We got an exclusive interview with one of those jailers, Preston Wills.

Wills calmly told us how from his first day he was taught to keep order in the jail by abusing prisoners. I was stunned to hear his matter-of-fact descriptions of the brutality that he says was condoned and encouraged by his superiors. Wills says the term was: "make 'em understand."

We were fortunate to find former inmates who willing to come forward and talk about what they'd been through.

It's important to remember that this is just a county jail. This is not a maximum security prison packed with murderers and rapists. Many people are brought there for misdemeanors, crimes like public drunkenness or unpaid parking tickets.

Two prisoners we interviewed were both in jail overnight. One says guards pummeled him, slammed him into a concrete wall and ripped his shoulder out of its socket. The other says he was beaten, strapped so tightly into a restraining chair that he had nerve damage, and then had a sheet pulled over his face and water poured on it until he couldn't breathe. When he finally went to the hospital days after his release, he says doctors found he was suffering from near-fatal kidney failure.

The county denies any wrongdoing in the Smith case and in the other cases of alleged abuse we reveal in our reports.

Despite initially agreeing to an on-camera interview, Sheriff George Payne changed his mind once he learned the Smith family had gotten the results of the second autopsy.

Instead, he released a statement saying, "I in no manner or form condone or encourage the use of excessive force by any individual employed by the Harrison County Sheriff's Department. As always, in the event that I become aware of suoh allegations, the incident is thoroughly investigated and reported to the proper investigatory entity."

Initially, Harrison County authorities planned to investigate Lee Demond Smith's death themselves. But Smith's family believed it would not be a fair investigation. So three weeks into CNN's investigation, the local district attorney asked the U.S. Justice Department to take over the case.

After the three-plus months CNN has investigated this case, I'd like to believe our reporting will force change at the jail. But I'm not optimistic.