A former Credit Suisse broker was on Monday convicted by a jury of fraudulently selling risky auction-rate securities in one of the first criminal prosecutions to emerge from the two-year-long credit crisis.

The guilty verdict against Eric Butler, 36, comes after a three-week trial in which prosecutors accused him and his former colleague, Julian Tzolov, of scheming to generate higher sales commissions by lying to clients about what kind of securities they were being sold.