Jamal Khashoggi
A man holds a poster of Saudi journalist Jamal Khashoggi during a protest organized by members of the Turkish-Arabic Media Association at the entrance to Saudi Arabia's consulate in Istanbul, Turkey, Oct. 8, 2018. Getty Images/ Chris McGrath

A United Nations investigator said on Wednesday that Saudi Arabia was responsible under international law for the "deliberate, premeditated execution" of Washington Post journalist Jamal Khashoggi in October 2018.

Agnes Callamard, the U.N. Special Rapporteur on extrajudicial executions, said there is "sufficient credible evidence" that Saudi Prince Mohammed Bin Salman and other senior officials bear responsibility for Khashoggi's death.

Callamard notes in the 101-page report the "extreme sensitivity" of weighing the criminal responsibility of the crown prince and Saud al-Qahtani, a senior adviser to the Saudi royal court.

She called on the head of the U.N. Antonio Guterres and the U.S. Federal Bureau of Investigation (FBI) to do further investigative work into the crimes. The U.S. Central Intelligence Agency concluded in November 2018 that the crown prince was behind the killing.

The report cites audio recordings that "suggest that Mr. Khashoggi could have been injected with a sedative and then suffocated with a plastic bag."

Saudi Arabian Foreign Minister Adel al-Jubeir shot back at the allegations.

"The report of the rapporteur in the Human Rights Council contains clear contradictions and baseless allegations which challenge its credibility," he tweeted Wednesday. Al-Jubeir said that the case should only be dealt with by the Saudi legal system.

The Trump administration has been criticized for not doing enough to investigate Saudi Arabian interests involved in the attack. Trump's son-in-law, Jared Kushner, frequently speaks with the crown prince over WhatsApp, CNN reported.

Khashoggi, a journalist and columnist for the Post, went to the Saudi Arabia consulate in Istanbul on Oct. 2, 2018, to obtain documents so he could marry his Turkish fiancée Hatice Cengiz.

Khashoggi had frequently criticized the crown prince.