The announcement came after difficult negotiations led the Police Department to enter a court agreement with the U.S. Justice Department last summer to address concerns that officers were too quick to use force.
Diaz said that after a 36-year career -- the past 33 with the Seattle Police Department -- he had planned to retire this year. A judge's acceptance of the monitoring plan last month provided a good opportunity to do so, he said.
"That monitoring plan is in place," he said. "It's time for me to let others move forward on that, but I wanted to make sure the hard work of the reform issues, that some of the innovation that I was really interested in was up and running."
Diaz was named interim chief in 2009, after his predecessor, Gil Kerlikowske, left to become President Barack Obama's drug czar. Diaz was given the job officially the next year and immediately faced difficulties, Mayor Mike McGinn noted.
Soon after his appointment, the department was tasked with tracking down a suspect who had attacked a lesbian couple in their South Seattle home, raping and stabbing both. One of the victims collapsed and died in the street after escaping the house naked and covered in blood.
Later that year, Officer Timothy Brenton was shot and killed as he sat in his cruiser following a traffic stop.
The next summer, an officer shot and killed Native-American woodcarver John T. Williams, who crossed the street in front of a patrol car.
The officer said Williams had ignored orders to drop a small folding knife he was carrying. Video from a dashboard camera showed that about six seconds elapsed from the time the officer got out of his car to the time he finished firing.
Surveillance video also showed other questionable incidents of force, including officers stomping on a prone Latino man while using racial epithets after mistaking him for a robbery suspect.
The Williams killing, which the department itself found unjustified, helped prompt the Department of Justice to examine the Seattle Police Department's use of force. The DOJ's report found officers were too quick to reach for weapons such as flashlights and batons, even when arresting people for minor offenses, and that when Seattle police used force, they did so unconstitutionally about 20 percent of the time.
The DOJ never fully explained how it arrived at that figure, and the Police Department bristled at it. Some officers continue to question it.
The city and DOJ sometimes butted heads over what changes should be made at the department. Diaz and the mayor promoted a reform plan they called 20/20, but the DOJ said it was too vague. Eventually, the sides agreed to a deal calling on the Police Department to revise its use of force policies and enhance training, reporting, investigation and supervision for situations involving the use of force.
McGinn praised Diaz on Monday for his commitment to reform. He touted programs Diaz instituted to give officers the discretion to send low-level offenders to social service programs rather than jail; to confront drug dealers and give them a choice between shaping up and being prosecuted; to add a mental health expert on staff to help officers; and to have officers spend more time out of their cars to deter crime in certain neighborhoods.
"He's been in charge of a department in transition, as we all know, but the achievements have been considerable," McGinn said.
But Diaz also drew criticism. City Councilman Tim Burgess, who is running for mayor, said Diaz was too slow to adopt new strategies for preventing crime and to embrace the changes sought by the DOJ. Burgess had said he would fire Diaz if elected.
A recent outside report commissioned by Diaz slammed the department for its handling of -- and lack of preparation for -- last year's May Day riots, when black-clad anarchists smashed the windows of downtown stores and banks.
"He was someone who was really good to work with, a humble leader and very accessible," said Chris Stearns, chairman of the Seattle Human Rights Commission. "We're in a real critical time, going through the first year of the consent decree. We've got a new community police commission that's starting to meet. We need a permanent chief in there who everyone can get behind."
Diaz, 55, joined the department in 1980 after serving three years as a criminal investigator in the Army.
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