William LaCorte keeps a half-dozen marble paperweights at his medical practice in this New Orleans suburb, engraved with images of checks from a lucrative sideline: suing companies for alleged health-care fraud.

Over two decades, the 65-year-old internist has filed 12 lawsuits accusing health-care companies of defrauding taxpayer-funded programs such as Medicare. Five of his suits have together led the government to recover hundreds of millions of dollars.

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Most claimants file just one suit. But at least 25 people or groups have filed five or more since 1986, says Stanford Law School professor David Freeman Engstrom, who studies such suits and represented a plaintiff in one against oil-and-gas companies from 2007 to 2009.