SAN FRANCISCO — After San Francisco City Attorney Dennis Herrera announced Thursday that his office had no idea who among the mayor and Board of Supervisors authorized the leak of a confidential legal memo from his office, the mystery was solved Friday when Mayor Gavin Newsom owned up to disclosing it.

Herrera had chided the mayor and the board in a press release Thursday after a legal memo on the city’s sanctuary policy was quoted in the San Francisco Chronicle . “Confidential legal advice is not intended to be fodder in political disputes,” stated the release, headlined “Herrera Issues Guidance to Board, Mayor Following Disclosure of Legal Advice.”