Octavio Montanero is a drug addict who was arrested and imprisoned for the murder of Detective Darryl Jennings, a crime he didn't commit. He was later murdered in prison under the orders of Eamon Murphy, who was Darryl's murderer.
His death was ruled as a suicide by the police according to Rika Harold, which the Organized Crime Control Bureau refused to believe and continued to investigate his death. (OC: "Partners In Crime")