OKLAHOMA CITY (AP) — A former investigator for an Oklahoma prosecutor has accused his ex-boss of ordering an illegal investigation into supporters of criminal justice reform, then firing him when he failed to find any wrongdoing.

The investigator, William Muller, has filed a "notice of claim" with the state and county against Oklahoma County District Attorney Prater, a first step toward a possible wrongful termination lawsuit.

In the claim, Muller alleges that Prater targeted the group Oklahomans for Criminal Justice Reform because of his opposition to its proposals. The claim alleges Prater i...