Protesters had been demanding for months that San Francisco Police Chief Greg Suhr be removed from office, but backed him despite several racially-charged incidents in the department.
That support ended on Thursday when Lee ask for, and received, Suhr's resignation.
The last straw appeared to have happened hours earlier when a police officer fatally shot a young black woman as he tried to arrest her for allegedly driving a stolen car that had crashed into a parked truck.
That shooting happened in the same neighborhood where months earlier five officers fatally shot a young black man carrying a knife.
After that shooting, and with the mayor's support, Suhr instituted reforms intended to cut down on police shootings.
At the same time, federal officials were asked to review the department's protocols.
But reforms were slow to take hold.
As recently as last month, three officers were discovered to have exchanged racist and homophobic text messages.
After receiving Suhr's resignation, the mayor made a brief statement at City Hall, writes the San Francisco Examiner:
"I have previously expressed confidence in Chief Suhr because I know he agrees with and understands the need for reform," Lee said. "He has demonstrated his commitment to instilling these reforms into the whole department, from the command staff to the cadets."
The mayor continued, "But following this morning's officer-involved shooting and my meeting with Chief Suhr this afternoon, today I have arrived at a different conclusion to the question of how best to move forward.
"The progress we've made has been meaningful, but it hasn't been fast enough. Not for me, not for Greg. That's why I have asked Chief Suhr for his resignation. And in the best interest of the City he loves so much, he tendered his resignation earlier today."
Lee appointed Suhr chief in 2011, a veteran of more than 30 years in the department. The Associated Press reports he rose through the ranks despite several missteps.
He was demoted from deputy chief to captain in 2009 after failing to file a police report after a female friend told him she had been assaulted by her boyfriend.
The city last year paid $725,000 to settle a wrongful termination lawsuit filed by a former department lawyer who recommended Suhr be fired for failing to report his friend's assault. When Suhr became chief, he fired the lawyer.
Suhr was also re-assigned from head of patrol in 2005 to guarding the city's water supply, which was widely viewed as a demotion.
Two years earlier, he was one of several officers indicted in the city's so-called "Fajitagate" for allegedly trying to cover up an investigation of three off-duty officers who had beaten up a waiter and took his bag of Mexican food. The indictment was tossed out.
On Thursday, Mayor Lee announce Suhr's replacement.
The San Jose Mercury News reports:
Lee appointed Commander Toney Chaplin as acting chief. A 26-year African-American veteran of the department, the mayor said Chaplin is committed to the city's diverse communities. He has served at Mission and Taraval stations, in the Gang Task Force, and ran the homicide division. He most recently established the department's new Professional Standards and Principled Policing bureau, which focuses on transparency and accountability, the mayor said.
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