The Supreme Court in the northwestern US state of Washington on Thursday ended use of the "racially biased" death penalty and immediately converted all death sentences to life imprisonment.
Washington, where there have been no executions since 2010, becomes the 20th state in which executions are banned.
The death penalty is not unconstitutional "per se," but it is "invalid because it is imposed in an arbitrary and racially biased manner," the state's top court unanimously ruled.
The death penalty has been "unequally applied -- sometimes by where the crime took place, or the county of residence, or the available budgetary resources at any given point in time, or the race of the defendant."
As administered in Washington state, the death penalty "fails to serve any legitimate penological goal," the court said.
The state's highest court issued the ruling while handling the case of Allen Eugene Gregory, sentenced to death for the rape and murder of a woman in 1996.
In his appeal Gregory included a study that showed the death penalty was applied differently from one court to another in Washington State and that, all things being equal, the probability of being sentenced to death was 4.5 times higher for African-Americans than for whites.
According to the Death Penalty Information Center the ruling directly affects eight people on the state's death row.
In their ruling, the justices noted that the state Supreme Court had already declared the death penalty unconstitutional three times earlier -- in 1972, 1979 and 1981 -- but that each time a new law was adopted.
Washington State has only carried out five executions since 1976 and Governor Jay Inslee, a Democrat, declared a moratorium on executions in 2014.
"This is a hugely important moment in our pursuit for equal and fair application of justice," said Inslee, commenting on the ruling.
The use of the death penalty is on retreat across the United States, where only 39 people were sent to death row in 2017, compared to 295 in 1998 or even 114 in 2010.
Of the 30 states in which capital punishment is still legal, there have been no executions in 16 of them since 1976.
Since the start of the year 18 inmates have been executed in the United States, 10 of whom were put to death in Texas.