And while the size of the alleged fraud spun by Mr. Stanford and his colleagues pales in comparison to Mr. Madoff’s scheme, the revelation that Stanford Group’s returns may, in fact, have been ephemeral is likely to further erode confidence among investors who place money with investment advisers.

Image Robert Allen Stanford, the chief of the Stanford Financial Group. Credit... Joe Skipper/Reuters

“I am extremely concerned. On a scale from one to 10  infinity,” said Brett Zagone, a Houston technology saleswoman who walked up to Stanford Group’s Houston offices Tuesday to find out what had happened to the money she had invested there.

At the St. John’s branch of Stanford’s Bank of Antigua, a long line of customers waited to withdraw money as the news spread, Reuters reported.

Regulators, too, are likely to face tough questions as more is learned about Mr. Stanford’s activities. Already under fire for missing several red flags over the years in the Madoff case, regulators could face similar questions as Mr. Stanford’s offshore banking activities caught the attention of law enforcement agencies dating as far back as 1998. In its complaint, filed in Federal District Court in Dallas, the S.E.C. accused Mr. Stanford, Mr. Davis and Laura Pendergest-Holt, the chief investment officer of both organizations, with misrepresenting the safety and liquidity of the C.D.’s. The Antiguan bank and its registered broker-dealer in Houston, which sold the C.D.’s, were also named. The bank claims $8.5 billion in assets and 30,000 clients in 131 countries, and the brokerage unit operates about 30 domestic offices.

Most witnesses, including Mr. Stanford, Mr. Davis and the Antigua-based bank’s president, failed to appear to testify and did not provide any documents shedding light on the assets. Stanford Group declined to comment.

Over the years, Mr. Stanford cultivated the profile of a successful American businessman, partly by burnishing his connections with athletes. For example, the pro golfer Vijay Singh signed a deal to make the firm’s logo, the Golden Eagle, the dominant brand on his apparel and golf bag. A spokesman for Mr. Singh’s agent declined to comment.