A court in Saudi Arabia has sentenced five people to death and jailed three others over the murder of the journalist Jamal Khashoggi last year.

Khashoggi, a prominent critic of the Saudi government, was killed inside the kingdom’s consulate in the Turkish city of Istanbul by a team of Saudi agents. The Saudi authorities said it was the result of a “rogue operation” and put 11 unnamed individuals on trial.

A UN expert said the trial represented “the antithesis of justice”. “Bottom line: the hit-men are guilty, sentenced to death. The masterminds not only walk free. They have barely been touched by the investigation and the trial,” Special Rapporteur Agnes Callamard wrote on Twitter.

A report released by Ms Callamard concluded in June that Khashoggi’s death was an “extrajudicial execution” for which the Saudi state was responsible, and that there was credible evidence warranting further investigation that high-level officials, including Crown Prince Mohammed bin Salman, were individually liable.

The prince denied any involvement, but in October he said he took “full responsibility as a leader in Saudi Arabia, especially since it was committed by individuals working for the Saudi government”.

A senior aide, Saud al-Qahtani, was sacked and investigated over the killing but not charged “due to insufficient evidence”, the public prosecution said. Former Deputy Intelligence Chief Ahmad Asiri was put on trial but acquitted on the same grounds.

The Turkish foreign ministry said the decision of the Saudi court was “far from meeting the expectations of both our country and the international community to shed light on the murder with all its dimensions and deliver justice”.

Khashoggi’s fiancée, Hatice Cengiz, called the Saudi announcement “not acceptable”.

The publisher of the Washington Post, for whom Khashoggi wrote columns, said: “The complete lack of transparency and the Saudi government’s refusal to co-operate with independent investigators suggests that this was merely a sham trial.”

A statement by the Saudi public prosecution said a total of 31 individuals were investigated over the killing and that 21 of them were arrested. Eleven were eventually referred to trial at the Riyadh Criminal Court and the public prosecutor sought the death penalty for five of them. Human Rights Watch said the trial, which took place behind closed doors, did not meet international standards and that the Saudi authorities had “obstructed meaningful accountability”.

On Monday, the Riyadh Criminal Court sentenced five individuals to death for “committing and directly participating in the murder of the victim”, according to the public prosecution’s statement. Three others were handed prison sentences totalling 24 years for “covering up this crime and violating the law”, while the remaining three were found not guilty.

The public prosecution said it would decide whether to review the court’s rulings and decide whether to appeal. The death sentences must be upheld by the Court of Appeal and the Supreme Court. Ms Callamard said in June that the five people facing the death penalty were Fahad Shabib Albalawi; Turki Muserref Alshehri; Waleed Abdullah Alshehri; Maher Abdulaziz Mutreb, an intelligence officer who the US said worked for Mr Qahtani; and Dr Salah Mohammed Tubaigy, a forensic doctor with the interior ministry.

The other six defendants were Mr Asiri, Mansour Othman Abahussain; Mohammed Saad Alzahrani; Mustafa Mohammed Almadani; Saif Saad Alqahtani; Muflih Shaya Almuslih, reportedly a member of the consulate staff.

According to interviews conducted by Ms Callamard, the defendants’ lawyers argued in court that they were state employees and could not object to the orders of their superiors, and that Mr Asiri insisted that he never authorised the use of force to bring Khashoggi back to Saudi Arabia.