The UN special rapporteur on extrajudicial or arbitrary executions, Agnes Callamard, has called on a probe into Saudi Arabia's chain of command in order to find organisers of the murder of Saudi-born journalist Jamal Khashoggi.

"Under international human rights law, the killing of Mr. Khashoggi was an extrajudicial execution for which the Kingdom of Saudi Arabia should be held responsible", Callamard said. "This case demands an investigation into the chain of command to identify the masterminds, as well as those who incited, allowed or turned a blind eye to the murder, such as the Crown Prince."

The UN special rapporteur said that the verdict was a "double shock" for her.

"Opposed to the death sentence, this is the first shock to me," she explained. "However, those who ordered the executions not only walk free but have barely been touched by the investigation and the trial. This is the second shock."

Callamard said that 18 Saudi officials were present in the Istanbul consulate for more than ten days and "cleaned up the crime scene."

"This is obstruction of justice and a violation of the Minnesota Protocol for the investigation of arbitrary killings", the rapporteur said.

Callamard continued to say that while the Saudi judge appeared to rule that the journalist's killing was an accident he still sentenced five people to death, "in a clear violation to international human rights law."

On Monday, a Saudi court sentenced five people to death for their involvement in Khashoggi’s murder. An additional three people were jailed for a combined total of 24 years. Three of the eleven people who stood trial were acquitted, including former top royal adviser Saud al-Qahtani, ex-Consul General in Istanbul Mohammed al-Otaibi and former Deputy Intelligence Chief Ahmed al-Asiri.

On October 2018, Khashoggi went missing after entering the Saudi consulate in Istanbul to obtain documents. Riyadh initially denied having any knowledge of Khashoggi's whereabouts but eventually admitted that the columnist was killed and his body dismembered inside the consulate.

A United Nations-led investigation concluded in February that Khashoggi’s killing was premeditated and perpetrated by Saudi officials. The Saudi monarchy has denied any role in the journalist's death, saying he was killed in a rogue operation.

Turkey and international human rights groups have slammed the ruling of a Saudi court in the trial over Khashoggi's murder trial.