The fiancée of dissident Saudi journalist Jamal Khashoggi has accused the US authorities of hiding the facts over his murder, and said their failure at transparency could permit other similar killings.

Hatice Cengiz, a Turkish writer and activist, said if the American government did not reveal what it knew, it would “show that the values of the US and all decent countries are empty and worthless”.

“The US Government should release all the information it has about the murder of Jamal so that the truth can come out,” she told The Independent in a statement. She added: “There is no reason to hide the facts.”

Earlier this year, a report by US intelligence said it believed that Saudi Arabia’s crown prince Mohammed Bin Salman, commonly known as MBS, had ordered the October 2018 killing, after becoming angered by Khashoggi’s criticism of the kingdom.

The report by the Office of the Director of National Intelligence (ODNI) “assessed” MBS approved the murder, and named a dozen of so Saudi agents it believed had killed the journalist inside the Saudi consulate in Istanbul, Turkey, before cutting up his body with a saw.

Yet, activists have accused the US of failing to make public what it knew in advance about a possible threat to the 57-year-old Washington Post columnist, who was a US resident. If the authorities were aware that his life was in danger, there was a legal obligation to warn him.

This week, Agnes Callamard, who investigated the killing in her position as UN special rapporteur on extrajudicial, summary, or arbitrary executions, told The Independent she believed it less and less likely the US was not aware of the threat.

“Everything that we are hearing is pointing to such a close nexus between the US and Saudi Arabia, including at an intelligence level,” said Ms Callamard, who is new secretary general of Amnesty International.

“And this, coming on top of the leaks very early on… It’s only a hypothesis, I have no material evidence, but it [increases] the likelihood of the US having captured intelligence regarding threats to Jamal.”

She added: “If they have information of any kind, and any source, regarding the killing; if they have information pointing to the extent of the responsibility of MBS, or the stops in Cairo, and they are not making it public – they are making themselves complicit of impunity.”

Ms Callamard spent six months investigating the murder, and said in her 2019 report that Saudi Arabia was responsible for his “premeditated execution”. She also said that there was credible evidence of the liability of MBS.

Saudi Arabia denied the prince was responsible and claimed Khashoggi had been the victim of a “rogue” operation.

Since the murder of Khashoggi, a fuller image has emerged of his life. He had been married in Saudi Arabia, and was engaged to marry Ms Cengiz. He also had a wife or fiancée in Washington DC, Hanan Elatr.

Last week, it was reported the phones of both Ms Elatr and Ms Cengiz had been targeted by NSO Group’s Pegasus spyware in the months before his killing.

Since his murder, Ms Cengiz, who had accompanied Khashoggi to the Saudi consulate and waited in vain for him to reemerge on what was the last time he was seen alive, had led an effort to secure justice for him.

Cengiz was last person to see Khashoggi alive - other than his killers

In 2020, she claimed on Twitter that “no-one has the right to pardon” Khashoggi’s killers after his two sons announced they had forgiven those responsible, after a trial widely seen as non-transparent.

She was also among those who sued MBS over the killing. Meanwhile, the US government is being sued by two organisations demanding it release what information it has about the killing, whether it was collected by the FBI, the CIA or any other government agency.

The White House did not reply to inquiries. The CIA and the ODNI referred to the US intelligence report from February, but failed to respond to the issue of whether the US had information in advance about the threat to Khashoggi.

The State Department said it could not comment on intelligence matters.

The Saudi embassy in Washington DC, its foreign ministry, and one of its US lawyers also did not respond to a request for comment.

In her statement Ms Cengiz said: “The US should be leading the way to hold the main and senior perpetrators of the killing to account.

“If they do not, it will allow this tragedy to happen again. It will show that the values of the US and all decent countries are empty and worthless.”

She added: “We must all unite now to make certain that there is justice for Jamal.”