SAN FRANCISCO, Oct. 11 (Xinhua) -- The Supreme Court of the U.S. western state of Washington Thursday struck down "unconstitutional" death penalty laws for the third time, making Washington the 20th U.S. state that has banned death penalty.

"The death penalty is invalid because it is imposed in an arbitrary and racially biased manner," the court said in a ruling, adding it "fails to serve any legitimate penological goals."

The ruling came in the case of the black man Allen Eugene Gregory, who was convicted of raping and murdering a 43-year-old woman in 1996. Gregory was removed from the death row and handed a life sentence instead.

The court said the death penalty is applied unequally, depending on the time of crime, the race of the defendant and the amount of money that is available to county prosecutors.

Washington State Governor Jay Inslee welcomed the court's decision. "Today's decision by the state Supreme Court thankfully ends the death penalty in Washington. This is a hugely important moment in our pursuit for equal and fair application of justice," he tweeted Thursday.

Inslee declared a moratorium on the death penalty in Washington State in 2014, when he said it's clearly that the use of capital punishment is inconsistent and unequal.

According to the American Civil Liberties Union (ACLU), a civil rights organization, black defendants in Washington are more than four times as likely to be sentenced to death as white defendants.

"It is a profound statement when every member of the Washington Supreme Court agrees that the death penalty is arbitrary, infected with racial bias, and must end," said Kathleen Taylor, executive director of the ACLU of Washington.