Mayor Ed Lee plans to announce Tuesday that he is hiring a veteran Los Angeles deputy police chief to lead the San Francisco force as it implements broad changes in the wake of several shootings of African Americans and Latinos, according to City Hall sources.

William Scott, who is 52 and African American, has been with the Los Angeles Police Department for more than 25 years and heads the department's 1,700-member South Bureau, a nearly 58-square-mile territory.

The selection of Scott is certain to surprise friends and critics of Lee alike, with the mayor looking outside the city rather than promoting acting Police Chief Toney Chaplin - which many city leaders expected, and the officers' union urged - or a member of his command staff.

But as much as Scott's longtime administrative experience figured into the decision - he did assignments in patrol, the detectives bureau, internal affairs and gang operations - we're told he was coveted as much for his work in the department's professional standards bureau dealing with police reform.

"He has been part of a department that during the last 10 years has undergone its own transformation, implementing a variety of reforms under a consent decree with the Justice Department," said one source familiar with the selection process.

Scott, whose appointment does not require confirmation by the Police Commission, is expected to be on hand Tuesday morning when Lee introduces him at a City Hall news conference.

Since the search began seven months ago, the perceived front-runner was Chaplin, who is also African American. Chaplin was elevated in May following the forced resignation of Greg Suhr, just hours after the fatal police shooting of an unarmed African American woman in a stolen car renewed questions about whether the Police Department had lost the confidence of minority communities in the city.

The department was already being reviewed by the U.S. Justice Department, which in October recommended 272 changes after concluding the force needed to better train, track and discipline officers. The Justice Department agreed to study the SFPD following the fatal police shooting last December of an African American man.More by Matier & Ross

Chaplin initially said he wanted to stay on as chief only temporarily, but he changed his tune within a few months after winning support from some black religious leaders and the San Francisco Police Officers Association. The union has been at loggerheads with the mayor's office, the Police Commission and community activists over the department's use-of-force policies in the wake of a string of deadly officer-involved shootings over the past couple of years.

The Police Officers Association even aired a radio ad in support of Chaplin, preferring an in-house candidate that they knew to someone from the outside. The union is still locked in a toxic political battle with the city's last outside chief, George Gascón, who is now San Francisco's district attorney. Like Scott, Gascón had served in Los Angeles under former Chief William Bratton.

As late as Monday, union President Martin Halloran described Chaplin as "the right chief at the right time."

But Chaplin faced questions over the strength of his educational credentials and his relative lack of experience. He didn't enter the command ranks until 2015, when he was promoted from lieutenant to commander. Plus, Chaplin lives in Castro Valley, and he indicated early in the process that he had no intention of moving to the city.

Sources tell us Scott, who is married and has three children, has committed to living in San Francisco. He likely will start in about a month at an annual salary of roughly $316,000.

Scott was an Army brat whose family eventually settled in Birmingham, Ala., where he attended the University of Alabama and got a degree in accounting, according to published reports. He began working for the Los Angeles force in 1989 and two years ago was promoted to deputy chief overseeing a section of the city that includes USC, the Port of Los Angeles and South Los Angeles, an area rife with homicides and gang violence.

Word of Scott's appointment comes at a crucial moment for San Francisco police. On Wednesday night, the Police Commission is scheduled to take up - and possibly vote on - a new set of use-of-force policies sharply opposed by the police union.

Officers would be prohibited from shooting at moving vehicles - a mandate that has been adopted in many places but, according to the police union, would leave officers with no option if a homicidal motorist started running people down.

The neck hold known as the "carotid restraint" would also be barred. But without first supplying officers with stun guns as an alternative, the cops would have no choice but to use more lethal force, the police union argued.

In all, 61 candidates applied for the chief's job. In recent weeks, the Police Commission whittled the list to 10. The remaining candidates were asked to submit an outline of how they would implement the reforms recommended by the Justice Department.

The commission narrowed its choice to three - a list that, in addition to Scott and Chaplin, included a female candidate believed to have been San Francisco Deputy Chief Denise Schmitt.

As for Chaplin, he is expected to stay in the department, though the new chief will be free to pick his own command staff.