OAKLAND — A federal judge on Tuesday granted secret government requests for leniency and sentenced a former East Bay private eye to eight years in prison for his role in a police scandal that involved extortion, robbery, prostitution and so-called “dirty DUI” stings.

Christopher Butler, a former Antioch police officer who ran Butler & Associates in Concord, received time off his expected sentence based on his behind-the-scenes cooperation in ongoing prosecutions, including in the recent indictment of San Ramon divorce lawyer Mary Nolan. Butler, 51, had faced a statutory minimum sentence of 10 years after pleading guilty in May to an array of crimes, including selling drugs stolen from police evidence, illegally wiretapping private individuals, and shaking down prostitutes. Federal sentencing guidelines recommended a sentence of more than 12 years.