Jamal Khashoggi was killed inside the Saudi consulate in the Turkish city of Istanbul. Photo: BBC/AFP

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 shadow cast by the grisly murder of Jamal Khashoggi has hung over Saudi Arabia's international reputation for more than a year now.