A UN human rights investigator has concluded that Saudi officials “planned and perpetrated” the “brutal and premeditated killing” of journalist Jamal Khashoggi – and that the kingdom undermined Turkey’s efforts to investigate his death.

“Evidence collected during my mission to Turkey shows prima facie case that Mr Khashoggi was the victim of a brutal and premeditated killing, planned and perpetrated by officials of the state of Saudi Arabia,” Agnes Callamard said in a statement Thursday.

The UN special rapporteur, who did not cite a specific official, also concluded that “Turkey’s efforts to apply prompt, effective and thorough, independent and impartial, and transparent investigations — in line with international law — had been seriously curtailed and undermined by Saudi Arabia.

“Woefully inadequate time and access was granted to Turkish investigators to conduct a professional and effective crime-scene examination and search required by international standards for investigation,” she added.

Khashoggi, 59, a US-based Washington Post columnist, was murdered Oct. 2 at the Saudi consulate in Istanbul, where he had gone to collect documents for his planned wedding.

Callamard, who led a team of three experts on a week-long mission to Turkey, said they had obtained access to part of “chilling and gruesome audio material” of his death obtained by the Turkish intelligence agency.

Her team was “not able to undertake a deep technical examination of this material” and didn’t have an opportunity to authenticate it independently.

Saudi officials did not immediately respond to a request for comment from Reuters about the report.

Riyadh has said Khashoggi was killed in a “rogue” operation but has repeatedly denied that Crown Prince Mohammed bin Salman, the country’s de facto leader, was involved in the death.

Late last year, a Saudi public prosecutor’s spokesman said that 21 Saudis had been taken into custody in the case, 11 of whom had been indicted and referred to trial. The prosecutor said authorities were seeking the death penalty for five of them.

Callamard she had “major concerns” about the fairness of proceedings for the Saudis facing trial and had sought an official visit to the kingdom.

She plans to present her final report to the UN Human Rights Council in June.

Khashoggi was strangled before being chopped into pieces by a hit team of 15 Saudis sent to Istanbul for the killing, according to Turkish officials, with local reports suggesting his remains were dissolved in acid.

The UN official’s announcement comes a day after the Saudi government contested a key element of a CIA assessment that concluded that Prince Salman likely ordered the murder.

A confidential report by private security firm Kroll prepared for the Saudi public prosecutor found that none of the WhatsApp messages exchanged between the crown prince and top aide Saud al-Qahtani on Oct. 2 concerned the journalist or his murder, according to The Wall Street Journal, which reviewed a draft.

The existence of those messages between Prince Salman and Qahtani, who is believed to have overseen the team that killed Khashoggi, was one piece of evidence cited in the classified CIA assessment.

Two US officials said this week that the CIA stands by its “medium-to-high confidence” assessment that Prince Mohammed personally targeted Khashoggi, a former Saudi insider-turned-critic, and likely ordered his death.

The Saudi public prosecutor hired Kroll to investigate the WhatsApp exchanges after the Journal on Dec. 1 reported details of the CIA assessment.

With Post wires