How IT helped bust New York's governor
"What really snared Spitzer was a money laundering investigation flagged by suspicious activity reports (SARs) that banks have to file with the Treasury ... The prostitution ring that counted Spitzer as a customer was investigated due to some shady bank accounts, checks and wire transfers with big totals ($39,000, $400,000 and others).
— ZDNet editor in chief Larry Dignan explains SARs in more detail.