In May 1970, Vance was appointed to serve as a commissioner in a landmark panel known as the Knapp Commission, which was formed and tasked by New York City Mayor John V. Lindsay with investigating systemic corruption at the New York Police Department. The Knapp Commission held televised hearings into police corruption and issued a final report of its findings in 1972. The work of the Knapp Commission led to the prosecution of police officers on charges of corruption and culminated in significant, if short-lived, reforms and oversight in respect of the police department, including the appointment of a temporary special prosecutor to investigate and prosecute corruption committed by NYPD officers, district attorneys, and judges.