Can an informant or victim request a copy of an investigative report even though the District Attorney did not file a case?

I was an informant for the Riverside County District Attorney regarding an investigation of real estate fraud, identity theft and theft. The defendant was not prosecuted due to the discretion of the Deputy District Attorney, however, the report is quite lengthy and has much information needed for proving matters in a civil case that I am involved in. I was told by the senior investigator on this case that I would be privileged to a copy of the report since I was the informant. I requested a copy of the report at the beginning of April and have been given the run around as to obtaining this copy. Can I legally pursue avenues to obtain this copy? Can I subpoena this report? I was told by USD law department that I can obtain a copy of this report even though a case was never filed.