The United Nations has lamented that the Saudi trial which convicted eight people of murdering journalist Jamal Khashoggi nearly two years ago lacked transparency.
Rupert Colville, spokesman for Office of the United Nations High Commissioner for Human Rights, said it was a "parody of justice" and spared "high-level" plotters.
"This was a very severe and gruesome crime, a horrendous crime.
"This is a case where there hasn't been proper transparency in the justice process and clearly those responsible should be prosecuted, and, and given sentences commensurate with the crime," Colville said.
He added that in such cases, "very lengthy jail sentences" would be appropriate.
He said that there's a whole issue of transparency in the conduct of the case.
The 59-year-old columnist for The Washington Post was killed and dismembered by a Saudi operatives group shortly after he entered the country's consulate in Istanbul, Turkey on October 2, 2018.
Riyadh offered conflicting narratives to explain his disappearance before acknowledging he was murdered in the diplomatic building in a "rogue operation."
On Monday, the Riyadh Criminal Court commuted death sentences, and handed down prison terms of up to 20 years to the accused, who were pardoned by the journalist's family. They were sentenced to death last year.
"The Saudi prosecutor performed one more act today in this parody of justice. But these verdicts carry no legal or moral legitimacy," tweeted Callamard, the UN special rapporteur on extrajudicial executions.
"They came at the end of a process which was neither fair nor just, or transparent," she said.
"The five hitmen are sentenced to 20 years imprisonment, but the high-level officials who organized and embraced the execution of Jamal Khashoggi have walked free from the start — barely touched by the investigation and trial," Callamard said in another tweet.
"As for the individual responsibility of the person on top of the State, the Crown Prince Mohammed bin Salman, he has remained well protected against any kind of meaningful scrutiny in his country."
"More than ever, the US Intelligence Services, including the Director of National Intelligence, must release the intelligence assessment of MBS [Mohammed bin Salman] responsibilities for the killing of JamalKhashoggi.
"Formal justice in Saudi Arabia cannot be achieved, truth-telling can," said the UN investigator.
Callamard, however, welcomed the death penalty being commuted.
"Had such sentences been carried out, they would have amounted to yet more arbitrary killings by the State of Saudi Arabia, and permanent silencing of key witnesses to the execution," she said.