SAN FRANCISCO (CBS SF) – A San Francisco police officer, identified as one of four involved in a scandal involving racist and homophobic text messages, has resigned from the force.

The San Francisco Police Department tells KCBS, 46-year-old Michael Robinson, a 23-year veteran, retired on Wednesday. The San Francisco Chronicle reports, he was transferred from the special victims unit to the horse mounted unit as an investigation into the text messages continues.

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“It is a very difficult situation for any police officer to see a future past this scandal,” Robinson’s attorney Tony Brass told the Chronicle. “It was a very tough decision. He loves the department and is very proud of his time working in the department.”

The text messages surfaced in a court filing by federal prosecutors in the case of former San Francisco police Sgt. Ian Furminger, who was convicted last December for robbing drug suspects during his stint as supervisor in the Mission District’s plainclothes unit. Prosecutors made the texts public last week, as they are looking to block Furminger from being released on bail during his appeal.

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All four officers were transferred to different positions after the text messages were discovered.

Meanwhile, the San Francisco Police Department has expanded its investigation to include 10 other officers, for their possible involvement in the case. San Francisco Public Defender Jeff Adachi and San Francisco District Attorney George Gascon have also agreed to review cases involving the officers.

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San Francisco Police Chief Greg Suhr said that he will look to fire the officers involved in the scandal if the investigation proves that the text messages were sent.