Saudi Arabia is responsible for the murder of Jamal Khashoggi in its Istanbul consulate last year, and there is “credible evidence” justifying an investigation into the role of the Saudi Crown Prince, Mohammed bin Salman, a UN expert said in a report released on Wednesday.

The expert, Agnes Callamard, also said that the UN secretary-general should establish an international criminal investigation to ensure accountability for the crime.

“There is credible evidence warranting further investigation of high-level Saudi officials’ individual liability, including the crown prince’s,” Callamard said in a 100-page report, issued after a five-month investigation.

Prince Mohammed, the day-to-day ruler of Saudi Arabia, was already widely suspected of having ordered the killing, a conclusion reached by western intelligence agencies.

But the report by Callamard, the special rapporteur on extrajudicial, summary or arbitrary executions for the UN human rights agency, is the most complete set of findings made yet public on the death of Khashoggi, a dissident Saudi writer who lived in the US.

“Evidence points to the 15-person mission to execute Khashoggi requiring significant government coordination, resources and finances,” Callamard wrote. “Every expert consulted finds it inconceivable that an operation of this scale could be implemented without the crown prince being aware, at a minimum, that some sort of mission of a criminal nature, directed at Khashoggi, was being launched.”

Khashoggi disappeared after visiting the Saudi Consulate in Istanbul on October 2 to obtain papers that would have enabled him to marry his Turkish fiancée, Hatice Cengiz, who was waiting outside.

Saudi officials said at first that Khashoggi had left the consulate alive and denied any knowledge of his whereabouts, but they later admitted that he had been killed in the building after what they said was a botched mission to bring him back to Saudi Arabia. A “local collaborator” disposed of his body, Saudi officials have said, but it has not been found.

“Khashoggi’s killing constituted an extrajudicial killing for which the state of the Kingdom of Saudi Arabia is responsible,” and may also have been an act of torture under international treaties, Callamard wrote.

“His attempted kidnapping would also constitute a violation under international human rights law.”

Saudi Arabia has put 11 officials identified as being linked to the killing on trial, but has conducted the proceedings in secret.

Callamard said that the trial failed to meet international standards. She called on Saudi Arabia to suspend the trial and cooperate with the UN in conducting further investigations and in deciding on the format and location of a trial.

Failing that, she said, it should carry out further investigations and allow global participation in the trial. Callamard coupled her recommendation with a scathing assessment of Saudi Arabia’s actions after the murder.

She said that Saudi Arabia’s investigation of the crime had not been conducted in good faith and that it may have amounted to obstruction of justice, citing evidence that officials hindered the work of Turkish investigators.