A California Supreme Court justice says the death penalty system in the nation's most populous state is dysfunctional, expensive and doesn't deliver justice in a timely way.

Associate Justice Goodwin Liu made the comments in an unusual opinion issued Thursday after the court unanimously upheld Thomas Potts' death sentence. He was convicted of killing an elderly couple in 1997.

But Liu wrote separately to express his concerns about the state of the death penalty system in California. Associate Justice Mariano-Florentino Cuellar joined him in the opinion.

Liu also said a 2016 ballot measure approved by voters to speed up executions wouldn't work without more funding.

The opinion comes two weeks after Democratic Gov. Gavin Newsom placed a moratorium on executions in the state. California hasn't executed anyone since 2006.

ORIGINAL STORY: 

California Gov. Gavin Newsom has signed an executive order putting a moratorium on executions in the most populous state.

Newsom signed the order Wednesday granting a reprieve to the state's 737 death row inmates for as long as the Democrat is governor. It doesn't change any convictions or sentences and won't allow anyone to be released from prison.

Newsom says his views on the death penalty were shaped 40 years ago through his grandfather's and father's advocacy on behalf of a wrongfully convicted man.

His order also repeals California's lethal injection protocols and closes the state's never-before-used death chamber at a state prison. California hasn't executed anyone since 2006.

President Donald Trump says Newsom is "defying voters." California voters narrowly approved a ballot measure to speed up executions in 2016.

Newsom says the order won't alter any convictions or allow any condemned inmate a chance at an early release.

"I do not believe that a civilized society can claim to be a leader in the world as long as its government continues to sanction the premeditated and discriminatory execution of its people," Newsom said in prepared remarks. "In short, the death penalty is inconsistent with our bedrock values and strikes at the very heart of what it means to be a Californian."

A prosecutor says Newsom is usurping voters' will.

Placer County Sheriff Devon Bell discussed his disapproval for the new suspension after one of his detectives was murdered in 2014.

He says the man who murdered the detective was deserving of the death penalty and he is concerned for other victims not receiving justice.

"It's my hope that the Governor reconsiders his decision and reflects on the will of the people of California to impose this sentence on those rare cases where the dreadful atrocities committed demand a higher level of justice."

California voters have supported the death penalty, most recently in 2016 when they narrowly voted to speed up the process. How to do that also has been tied up in litigation.

California is the sixth state where a governor has enacted a moratorium. 

(The Associated Press, CBS News contributed to this report.)