Gov. Gavin Newsom said Thursday that he intends to commute all California death sentences, declaring that “state-sanctioned killing is incompatible with” values in America’s most populous state.

In an open letter to constituents, Newsom said taking the step is “among the most difficult of my career.”

“I take this action because I firmly believe that state-sanctioned killing is incompatible with California’s values,” he said.

California has not put a prisoner to death since Jan. 17, 2006, when Clarence Ray Allen was executed via lethal injection.

Newsom said his executive action would affect the “548 people now under death sentence in California,” making for “the largest death row in the Western Hemisphere.” The move, however, requires the state Supreme Court to approve resentencing in cases in which people have more than one felony conviction, which Newsom said amounts to 382 of the prisoners on death row.

“I respectfully request that the Court issue its recommendation by the end of this year so that I may act before the end of my term,” Newsom, who is term-limited and leaves office in January, wrote in a letter Thursday to the justices.

There were 561 inmates on death row as of Tuesday, according to Department of Corrections records. In 2019, when there were 737 inmates awaiting execution in the state, Newsom ordered a moratorium on all of those cases. In a statement at the time, he said the death penalty was discriminatory, provided no public safety benefit and wasted billions.

Richard Allen Davis, who was convicted in the murder of 12-year-old Polly Klaas in 1993, is one of the inmates still on California’s death row.

Polly had been abducted at knifepoint from her home in Petaluma, north of San Francisco, during a slumber party. The case drew national attention after it triggered a massive search that eventually led investigators to Davis, who then directed police to the girl’s body in a shallow grave.

Marc Klaas, Polly’s father, said Newsom’s decision is a “knife in the back” to him and other victims’ families who believe death row prisoners were lawfully sentenced.

“It’s unbelievably disappointing,” Klaas told NBC News. “I was told that when this guy was sentenced to death that this was a system we can trust. But here we are, 33 years later, and it’s a system we can’t trust.”

Newsom’s proposal was embraced by death penalty abolitionists, human rights advocates and faith communities.

“This is a day that will be remembered in California’s history and resonate globally for years to come,” Amnesty International USA Executive Director Nadia Daar said in a statement.

“The death penalty should be abolished, everywhere. Today marks a significant moment for human rights in California and across the country,” Daar said.

The president of the National Association of Criminal Defense Lawyers cited “countless” studies that she said show that the death penalty doesn’t deter crime and called the move a “decision of historic moral clarity and courage.”

“The death penalty is unjust, uncivilized, and inconsistent with the fallibility of our justice system,” Melissa “Missy” Owen said in a statement.

Since the U.S. Supreme Court ended a brief pause on capital punishment with its landmark 1976 ruling in Gregg v. Georgia, there have been 1,687 state executions, according to Death Penalty Information Center records.

Texas has carried out the most, 603, while California has carried out just 13.

“Governor Newsom’s announcement marks a decisive moment in the history of the death penalty in the United States,” Death Penalty Information Center Executive Director Robin Maher said in a statement. “Though other governors have granted universal clemencies, none have been at this scale.”

Newsom, a Democrat, is frequently mentioned as a possible presidential candidate in 2028, and the timing of his announcement isn’t lost on Klaas.

“We’re talking about serial killers, we’re talking about spree killers, we’re talking about cop killers, we’re talking about child killers,” Klaas said. “Why, two days after the midterms, does Gavin Newsom feel the need to commute these sentences? Who benefits from this?”

In a statement, the California District Attorneys Association condemned Newsom’s decision, saying he replaced individual sentencing decisions that were reached after extensive legal proceedings “with a single executive decision that makes no distinction among the crimes committed, the circumstances of the offenders or the victims whose lives were taken.”

“With the stroke of a pen, Governor Newsom has disregarded the decisions of hundreds of jurors and judges, and the anguish of families who lost loved ones to the worst crimes imaginable,” said the association’s president, Monterey County District Attorney Jeannine M. Pacioni.

San Luis Obispo County District Attorney Dan Dow said Newsom’s action is an affront to the families of victims, whose killers were brought to justice by his office.

“Governor Newsom just told the families of Rachel Newhouse, Aundria Crawford, Kesha Gurke and every other innocent victim of California’s 548 condemned killers that the killers’ lives matter more,” Dow said in a statement as immediate past president of the California District Attorneys Association.

“Juries chose justice case by case, voters chose it five times, and one outgoing governor is trying to erase it all with a pen. This is a sickening abuse of power,” he said.