Kate Brown announced their death sentences would be changed to life in prison without the possibility of parole, most likely using her executive clemency powers for the last time as governor, NBC News reports.

She criticised capital punishment in a statement, saying the death penalty "cannot be and never has been administered fairly and equitably".

"I have long believed that justice is not advanced by taking a life, and the state should not be in the business of executing people - even if a terrible crime placed them in prison," Ms Brown said.

"Unlike previous commutations I've granted to individuals who have demonstrated extraordinary growth and rehabilitation, this commutation is not based on any rehabilitative efforts by the individuals on death row.

"Instead, it reflects the recognition that the death penalty is immoral".

She said the commutations were consistent with a moratorium on the death penalty that Governor John Kitzhaber, a Democrat, initiated in 2011.

She added: "I also recognise the pain and uncertainty victims experience as they wait for decades while individuals sit on death row - especially in states with moratoriums on executions - without resolution.

"My hope is that this commutation will bring us a significant step closer to finality in these cases."

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Last year, Virginia became the most recent state to legislatively abolish the practice, opting instead for a sentence of life imprisonment with no possibility for parole, data from the National Conference of State Legislatures reveals.

The death penalty was first legalised in Oregon in the 19th century, but it has been abolished and reinstated three times since then. It was most recently reinstated in 1984, with two executions taking place since then, in September 1996 and May 1997.

Ms Brown, a Democrat who is term-limited, took office in 2015 and will be succeeded in January by Democrat Tina Kotek. She was also ranked this year with the highest disapproval ratings of any governor in the country.

The order takes effect on Wednesday.