BALTIMORE (AP) -- Tens of thousands of prospective college students sent in money as part of a scholarship scam that fraudulently informed them they had won money for school, according to a federal indictment.

"Congratulations!" read the letters mailed to students around the country. "You have been selected by the National Scholarship Program."

Thousands sent checks to 10 programs operated by Christopher Nwaigwe, prosecutors say. The indictment filed Monday accuses him of mail fraud involving more than $500,000.

Since 1991, the bogus letters have led students from nearly every state to believe they had won grants worth $2,500 to $7,500, the indictment said.

Respondents were asked to send a fee of $10 to $100. In most cases, after the fee was paid, they never heard from Nwaigwe again, the Federal Trade Commission contends.

More than 50,000 people sent checks, said Paul Trimbur, a spokesman for the U.S. Postal Inspection Service. Prosecutors say none of the money has been recovered.

Nwaigwe, a 37-year-old Nigerian immigrant, ran several scholarship search companies out of Washington and Baltimore, according to the FTC. He violated a 1994 court order to stop the solicitations, court papers show.

Nwaigwe apparently is the first person to be prosecuted as a result of the FTC's eight lawsuits nationwide that have sought to block the operation of suspect scholarship companies. He was being held in Massachusetts and will be returned to face trial in Maryland.