The Los Angeles County Board of Supervisors this week approved District Attorney George Gascon’s request to appoint a special prosecutor to assist with cases of alleged police misconduct.

Gascon plans to appoint former federal prosecutor Lawrence Middleton for a four-year term at a cost of no more than $1.5 million annually, according to his letter to the board.

While campaigning, Gascon promised to reevaluate fatal officer-involved shooting cases that his predecessor, Jackie Lacey, declined for prosecution.

In his letter, Gascon said the appointment is needed “to promote public confidence in the decision-making process and the outcome of any such investigations’’ and would be “a positive step in rebuilding relationships in our community.’’

Middleton has more than 30 years of experience as a trial lawyer and led several divisions or sections of the U.S. Attorney’s Office for the Central District of California, which consists of Los Angeles, Orange, Riverside, San Bernardino, Ventura, Santa Barbara and San Luis Obispo counties.

Middleton was part of the team of lawyers who prosecuted the federal case against four Los Angeles Police Department officers charged in the 1991 Rodney King beating. All four were acquitted of state charges of excessive force; two of the four were subsequently convicted of federal civil rights violations.

The decision to appoint a special prosecutor comes as Gascon defends his moves to push through new policies that include no longer pursuing death sentences, not prosecuting juveniles as adults and doing away with most sentencing enhancements.

Though praised by many criminal justice advocates, the changes have also prompted condemnation and legal action from the union that represents county prosecutors and some victims’ rights groups who say Gascon is undermining public safety.