Even among the legions of successful young investors operating on Wall Street in the headiest days of the bull market, David Bloom, 23, stood out as a precocious hotshot. Armed with little more than a good line and glib self- assurance, the son of a Manhattan pizza-restaurant owner persuaded scores of clients to give him some $10 million so that he could play the stock market on their behalf. For some time, Bloom's clients were satisfied: quarterly reports for their accounts showed savvy trades and fat profits.
What no one realized was that, according to the Securities and Exchange Commission, the...