Still, the medicial equipment and HIV-infusion schemes alone add up to at least $7 million in Medicare fraud daily in South Florida, where a sprawling cast of illegal HIV-therapy clinics, bogus suppliers, inner-city patient recruiters, complicit doctors and devious billing companies have even used the names of dead doctors to bilk the U.S. government out of billions of Medicare dollars.

''I knew Miami was bad, but I was shocked when I got here,'' said Timothy Delaney, assistant special agent in charge of the FBI's office in Miami and the head of the bureau's national healthcare fraud program from 2000 to 2004. ``There is fraud here like nowhere else in the country. Los Angeles is second, but nowhere like it is here.''

South Florida's U.S. attorney, R. Alexander Acosta, placed much of the blame on Medicare and its system of screening bills, saying its poor oversight forces authorities to chase criminals long after they have absconded with taxpayer dollars. Little of the money is recovered.

''At a time when we're trying to find billions of dollars to pay for healthcare in this country, it's disgusting that so much money is being wasted because of Medicare fraud,'' Acosta said.

Kimberly Brandt, director of program integrity at the Centers for Medicare and Medicaid Services, said there's only so much the agency can do to protect the system because of limited resources. Congress has appropriated $720 million to combat fraud, with no increase in the past three years. That's a small piece of Medicare's $432 billion annual budget.

''I think the important thing for people to understand is that this didn't happen overnight, and it's not something Medicare could have detected overnight,'' she said.

Federal authorities are often unable to track down Medicare fraud culprits who flee the country.

A Miami Herald review of FBI, U.S. attorney and federal court records found that at least 56 of the roughly 700 Medicare fraud defendants are fugitives -- with at least 18 suspected of having fled to Cuba during the past five years. The others went to Mexico, the Dominican Republic, Colombia, Canada, Europe or are still in Florida.

Federal authorities and experts who have followed Medicare fraud say the South Florida perpetrators are not unlike segments of immigrant groups in other major cities who band together to abuse the system because of an implicit trust.

Cuban immigrants make up the vast majority of defendants prosecuted on charges of submitting billions of dollars in false Medicare claims since 2004, records show.

Among them: The Benitez brothers, charged with defrauding Medicare by billing $110 million in false claims for HIV-drug infusion treatments at their dozen clinics in Miami-Dade County. Medicare paid their companies about $84 million between 2001 and 2004, according to federal prosecutors.

The three brothers spent their ill-gotten gains on homes, helicopters, hotels, apartments, boats, even a water park -- all in the resort area of Bavaro, Dominican Republic, according to federal authorities.

After being indicted on federal fraud charges in Miami in late May, Carlos, Jose and Luis Benitez used their Cuban passports to travel from South Florida to the Dominican Republic, then to Cuba. With help from Dominican authorities, the Justice Department is seizing their properties and freezing their bank accounts on the island.

The FBI's Delaney and Medicare's Brandt said that illegal healthcare operators of Cuban descent are among several pockets of immigrant groups involved in similar scams in Los Angeles, Houston and New York.