Alameda County District Attorney Nancy O'Malley announced Tuesday that she will not seek re-election to a fourth term.

Her current term ends at the beginning of 2023. She has been working in the Alameda County District Attorney's Office for 37 years, and as district attorney since 2009.

Her office did not say why she is leaving or what she plans to do afterward. She released a public statement Tuesday, mainly describing her accomplishments in office.

"I could not be more thankful for the career I have had in the best District Attorney's Office in the state and certainly one of the best in the nation," she said in the statement.

O'Malley added that the office is well-respected by many and its respect is well-earned.

But this year she has been criticized for not charging former BART Police Officer Anthony Pirone for the death of Oscar Grant and reportedly a recall campaign was going to be waged by the Grant family. In about 12 years, O'Malley has charged one police officer for a criminal offense for actions on duty.

She joined the district attorney's office in 1984 and was the first woman elected as district attorney in Alameda County.

Her office said her legacy reaches far and wide, including the expansion of the victim/witness division and the opening of the Family Justice Center.

The center serves primarily women and children who have been victims of domestic violence, sexual assault or human trafficking, child abuse or elder/dependent care abuse.

O'Malley introduced in 2009 what has become a national model for anti-trafficking initiatives, called H.E.A.T. (Human Exploitation and Trafficking) Watch.

She also created an academy for high school juniors and seniors to help them find their passion. All the participants have gone on to college.

O'Malley led an initiative at the state and national levels to test forensic sexual assault kits, which were going untested in police hands.

She said her office has also created "more alternative courts to incarceration than any other county in the state and perhaps the country, per capita."

"We have consistently strived to ensure that the criminal justice system in California and Alameda County is more responsive, more aware and more humane for those who are accused, for victims of crime and for those who witnessed crime," O'Malley said.

Among the officials to publicly acknowledge O'Malley upon her announcement Tuesday was U.S. Rep. Eric Swalwell (D-Livermore), whose career as a deputy district attorney with the county included nearly three years during O'Malley's tenure.

"For 37 years Nancy O’Malley has served the cause of justice in Alameda County courtrooms and inspired criminal justice reforms across America. I am saddened to hear she will no longer serve as District Attorney, but we are so fortunate for the commitment she’s made throughout her career to help victims of domestic violence, human trafficking, and sexual assault," Swalwell said.

"For me, Nancy has played many roles: hiring attorney, boss, mentor, friend, and most recently, wedding officiant. As Nancy’s service to the office comes to an end next year, her work to serve justice will go on. I’m excited for what’s next," he added.

O'Malley's decision sets the stage for what could be a highly competitive 2022 campaign season to become the county's next top prosecutor. The primary election is in June 2022, with a runoff likely to occur in the general election that November.

Editor's note: Weekly editor Jeremy Walsh contributed localized details to this story.