Oakland police Chief Sean Whent is leaving his post after 19 years with the department, Mayor Libby Schaaf announced late Thursday night.

Schaaf and City Administrator Sabrina Landreth announced the resignation of Whent and the appointment of BART Police Chief Ben Fairow as interim chief in a statement released Thursday. More details about the transition will be revealed at a news conference Friday at 9 a.m. No official reason has been given for the sudden departure. Reporters from the East Bay Express tweeted that Schaaf was poised to fire Whent.

Fairow was sued last year by the widow of the late detective Sgt. Thomas "Tommy" Smith Jr., alleging that BART chiefs routinely send officers into high-risk search areas without properly trained SWAT officers. Smith was killed accidentally by a colleague during an apartment search of a robbery suspect in Dublin.

The mayor didn't acknowledge any of that in her prepared statement.

“Sabrina and I are grateful to Chief Whent for his dedication and service,” Schaaf said in the statement. “Chief Whent’s decision to resign was a personal choice which we respect.”

Whent said he is proud to have served Oakland over the course of two decades.

“When I took this job three years ago as interim chief, I vowed to help move the department forward and make Oakland safer by forging a stronger relationship with members of this diverse community," he said in a statement. "I am proud to have done that. I know that the vast majority of the men and women who work for the Oakland Police Department share this commitment and will continue to demonstrate it with every call for service.”

City Councilwoman Lynette Gibson McElhaney said she was shocked.

"I'm grateful for the Chief's service and am sorry to see him leave the Oakland Police Department," she said. "I think this chief was committed to making structural changes. I think it is a loss for our city."

Gibson McElhaney said she hopes Whent's replacement "will continue the good work he has done" but she worries "this could be a setback."

Whent's departure comes just weeks after Greg Suhr stepped down as police chief in San Francisco.

Groups such as the Anti-Police Terror Project, however, cheered the sudden announcement. On its Facebook page, the group wrote that this is a "victory the people should claim." They cited an internal sexual misconduct investigation into officers with an underage girl, among the shootings of black suspects, as two of the reasons they are happy to see him go.