Oakland detective whose girlfriend transcribed recordings cleared by DA

A line of police cruisers are seen in the depot at the Oakland Police Department in Oakland, CA Thursday, March 17, 2016. A line of police cruisers are seen in the depot at the Oakland Police Department in Oakland, CA Thursday, March 17, 2016. Photo: Michael Short / Special To The Chronicle 2016 Buy photo Photo: Michael Short / Special To The Chronicle 2016 Image 1 of / 1 Caption Close Oakland detective whose girlfriend transcribed recordings cleared by DA 1 / 1 Back to Gallery

Alameda County prosecutors said Thursday they have concluded that Oakland police Sgt. Mike Gantt broke no laws when he had his girlfriend transcribe recordings from criminal investigations for him, but an independent city investigator is looking into whether the practice broke internal police rules.

Gantt, a veteran homicide detective, came under fire this month after his girlfriend apparently got angry with him and made references to his cases on social media, sources told The Chronicle. The revelation — which is apparently unrelated to sexual misconduct and revolving chief scandals besetting the Oakland Police Department — cast into doubt some investigations Gantt had worked on, but District Attorney Nancy O’Malley said in a news release Thursday that she found nothing that corrupted them.

“After a thorough review of all matters involving Sgt. Gantt, the office finds that, while Sgt. Gantt may have violated internal departmental policy, no criminal conduct occurred,” O’Malley wrote. “There is no provision in the Penal Code that prohibits engaging third-party transcriptionists.

“Likewise, we have no reason to believe that the investigation was mishandled in any way that compromises past or current criminal prosecutions. We stand behind the integrity of each of these criminal cases.”

O’Malley said her office interviewed “the third party” — Gantt’s girlfriend — about the transcriptions, and determined she had typed up audio recordings between May 2013 and January 2014. That, O’Malley said, involved 10 criminal cases, seven of which were resolved by jury trial or guilty plea and three of which are pending.

Gantt gave the “third party” CDs to transcribe on his laptop, O’Malley wrote. “She ... never saw any other documents or paperwork including the police report, any criminal history, any DMV information or Sgt. Gantt’s notes.”

Gantt is on administrative leave while an investigator hired by the mayor and the city administrator conducts a probe, a source told The Chronicle.

Kevin Fagan is a San Francisco Chronicle staff writer. Email: kfagan@sfchronicle.com