SAN FRANCISCO (KRON) – Officer Michael Robison of the San Francisco Police department has resigned amid an investigation of his text messages in 2011 and 2012 that targeted blacks, Mexicans, Filipinos and gays.

Robison isn’t the only one under fire. A lawyer says three other officers are under investigation for their involvement.

In the preliminary stages of the investigation Robison was transferred from the Special Victims Unit to the horse-mounted unit.

Mayor Ed Lee said, “It is both shocking and disturbing to hear that four San Francisco police officers are under investigation for such heinous and despicable statements.”

“If these statements are attributable to any San Francisco police officer, I join Police Chief Greg Suhr in seeking nothing less than termination,” Lee said in a statement.

According to the San Francisco Chronicle, Robsion is openly gay. Robison is resigning after his texts were made public.

District Attorney George Gascon said he was “deeply disturbed by these text messages” and said that “in order to ensure our criminal justice system is fair and equitable,” his office will assess every prosecution in the past 10 years in which the officers participated.