"We could challenge it, and I am pretty sure we would win," he said. "But is there any point given that we can't challenge a reprieve? We have to think about that."
Newsom's action leaves the death penalty law in place. Prosecutors may still seek death sentences, and appellate courts will continue to have to review them.
Scheidegger said a victim has the right under Prop. 66 to challenge Newsom's decision to discard the protocol and shut down the death chamber.
Attorney General Xavier Becerra, who has said he supports the death penalty, also could challenge it, Scheidegger said, adding, "But there is no chance in hell of that."
He said Becerra has been "dragging his feet" in litigation to restart executions. "So for the attorney general to take any positive action would astonish me," he said.
Becerra, in a prepared statement, praised Newsom for his "bold" action.
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"We must always strive to sustain a criminal justice system that reflects our values of fairness and equality," Becerra said. "Governor Gavin Newsom's action today represents a bold, new direction in California's march toward perfecting our search for justice."
Death penalty prosecutions have been declining in California and in the nation as prosecutors have become more selective in charging, and homicide rates have declined.
San Luis Obispo County District Attorney Dan Dow said Newsom's executive order would not affect his decisions on whether to seek the death penalty in the future.
"This office will continue to look at it on a case-by-case basis," Dow said. "The governor cannot strike the law, and death sentences are still valid."