An Illinois woman mourns her two young daughters, swept to their deaths in Hurricane Katrina’s floodwaters. It’s a tragic and terrifying story. It’s also a lie.

An Alabama woman applies for disaster aid for hurricane damage. She files 28 claims for addresses in four states. It’s all a sham.

Two California men help stage Internet auctions designed to help Katrina relief organizations. Those, too, are bogus.

More than 18 months after Hurricane Katrina decimated the Gulf Coast, authorities are chipping away at a mountain of fraud cases that, by some estimates, involve thousands of people who bilked the federal government and charities out of hundreds of millions of dollars intended to aid storm victims.

The full scope of Katrina fraud may never be known, but this much is clear: It stretches far beyond the Gulf Coast, like the hurricane evacuees themselves. So far, more than 600 people have been charged in federal cases in 22 states — from Florida to Oregon — and the District of Columbia.

The frauds range in value from a few thousand dollars to more than $700,000. Complaints are still pouring in and several thousand possible cases are in the pipeline — enough work to keep authorities busy for five to eight years, maybe more.

“The reason we’re seeing such widespread fraud is individuals were evacuated to all 50 states. Katrina was a national phenomenon,” says David Dugas, U.S. attorney in Baton Rouge, La., and director of a command center that’s part of a special Hurricane Katrina Fraud Task Force. “Everybody knew what was going on. Therefore, criminals knew what was going on.”

Disaster aid was sent to inmates who applied from prison and to people who claimed property damage and provided addresses of vacant lots or cemeteries, among many abuses documented in Government Accountability Office reports.

“We found several dozen schemes. There are probably a lot more out there,” says Gregory Kutz, a GAO investigator who has testified about Katrina fraud six times on Capitol Hill. “The real clever ones cover their trail and disappear and they’ll never be caught.”

GAO undercover investigators demonstrated how easy it was to cheat the system: Using phony names, Social Security numbers, and addresses of damaged residences — such as the 13th floor of a two-story building — they still received several checks.

While many people filed bogus claims, the growing roster of the accused goes beyond the usual con artists. It includes employees of the Federal Emergency Management Agency and the Army Corps of Engineers, other public officials, business owners, even temporary workers for the Red Cross.

“You can find criminals in every walk of life and that’s what we’re seeing here,” Mr. Dugas says.

The GAO has referred more than 22,000 potential cases of fraud to the Katrina task force, though Mr. Dugas says the majority probably will not pan out. In a recent audit, the GAO also concluded FEMA had recovered less than 1% of some $1 billion investigators claim was fraudulent aid.

FEMA believes the fraud total may be inflated but says it won’t have an estimate until later this year. Mr. Kutz’s response: “I don’t think they know the magnitude of the problem.”

A recent Associated Press analysis of government data obtained under the federal Freedom of Information Act suggested the government might not have been cautious enough as it doled out nearly $5.3 billion in aid to storm victims. The analysis found the government made more home grants than the number of homes in one of every five neighborhoods after Katrina.

The nature of Katrina fraud already has shifted as the Gulf Coast has begun reconstruction. Mr. Dugas says there now are more elaborate schemes with bigger losses.

In Mississippi, for instance, three people, including a Florida contractor, recently pleaded guilty to falsifying records of Katrina debris cleanup and billing the federal government $716,677 for the work.

Charges also have been filed against organized rings in Florida, Texas, and Oregon.

The Oregon case offers a textbook example: Ten people have pleaded guilty to applying for disaster checks. In their scheme, a few ringleaders recruited friends, neighbors, and relatives, then split the proceeds. They collected about $324,000. None had any connection to Katrina.