United Nations Secretary General Antonio Guterres should launch an international criminal investigation into the killing of Saudi journalist Jamal Khashoggi last October, an independent rights expert said on Wednesday. In a fresh report on the killing, UN special rapporteur on extrajudicial, summary or arbitrary executions Agnes Callamard urged Mr Guterres to "initiate a follow-up criminal investigation into the killing of Mr Khashoggi to build-up strong files on each of the alleged perpetrators and identify mechanisms for formal accountability, such as an ad hoc or hybrid tribunal." <em>Washington Post</em> columnist Khashoggi was last seen at the Saudi consulate in Istanbul on October 2, where he was to receive papers ahead of his wedding, before he was murdered. The report stressed that "no conclusion is made as to guilt. The only conclusion made is that there is credible evidence meriting further investigation, by a proper authority, as to whether the threshold of criminal responsibility has been met." Riyadh blamed the murder on rogue agents. Saudi prosecutors have said around two dozen people implicated in the murder are in custody, with death penalties sought against five men. Ms Callamard has been conducting what she has described as "an independent human rights inquiry" into Khashoggi's death. For her investigation, Ms Callamard said that, among other things, she had viewed CCTV footage from inside the consulate of the killing itself. UN special rapporteurs are independent and do not speak for the world body. Commenting on social media about the report’s findings, Adel Al Jubeir, Saudi Arabia’s Minister of State for Foreign Affairs, tweeted that it contained “clear contradictions and unfounded allegations” and said that the kingdom’s judicial process should be respected by commentators and observers outside the country.