California Gov. Gavin Newsom said Thursday that he plans to commute death sentences for 548 people facing execution by the state, allowing them to serve life in prison without the possibility of parole.

Newsom’s office said his actions would benefit 529 men and 19 women, if all the commutations are finalized. The state’s Supreme Court must approve the resentencing for those with more than one conviction. Newsom said 382 people on death row had more than one conviction.

“Many Californians feel that those who commit brutal crimes deserve to die. But as Governor, I have concluded the state cannot morally kill them,” Newsom said Thursday in a letter to Californians.

The governor, a Democrat who is leaving office in January due to term limits and is considering a run for president, called the decision the most difficult of his career. He said he spoke to crime victims and public safety experts about it.

“I deeply respect the views of those who will strongly disagree with my decision, including some families of victims who have suffered the worst possible loss,” he said.

If approved, it would be the largest mass commutation in U.S. history and reduce the number of people on death row nationwide by nearly 30%, according to the nonprofit Death Penalty Information Center.

A moratorium on executions in California has been in place since 2019, when Newsom signed an executive order two months into his first term. But capital punishment remains part of state law. California voters in 2016 rejected a ballot measure to ban capital punishment, with 53% voting against it.

The most recent execution in the state was in 2006, according to the California Department of Corrections and Rehabilitation. Newsom’s 2019 order repealed California’s lethal injection protocol and closed the execution chamber at the San Quentin Rehabilitation Center, the oldest operating state prison.

Capital punishment has been in the national spotlight recently after the botched execution of Christa Pike, a Tennessee inmate who survived a double-dose lethal injection in September. The state’s Republican governor, Bill Lee, halted all executions in the state for the remainder of the year.

Those currently on California’s death row include serial killers and rapists. Newsom said he considered not granting clemency to those who committed “the ‘worst of the worst’ crimes,” but decided against it.

“Attempting to distinguish among crimes and offenders for clemency would inadvertently create two classes of murder victims—those whose perpetrators deserve the death penalty and then the rest,” he said.

Those who are granted a commutation won’t be eligible for release, the governor said. “These offenders will die in prison but not by our hand,” Newsom said.