A U.N. investigation into the brutal slaying of Jamal Khashoggi released Wednesday provides the clearest picture yet of the journalist’s final moments inside the Saudi Consulate in Istanbul, refocusing attention on Saudi Crown Prince Mohammed bin Salman and his crackdown on dissidents.

The months-long investigation by Agnes Callamard, a human rights expert at the United Nations, faulted the United States and other countries for not exerting enough pressure on Saudi Arabia despite “credible evidence” of the likelihood that ­Mohammed was involved in Khashoggi’s killing.

She called for sanctioning and freezing the prince’s assets until he is either cleared or definitively implicated. 

With access to audio recordings provided by Turkish intelligence, Callamard laid out in graphic detail how Saudi government agents prepared to kill and dismember Khashoggi. The planning started days before the killing, after Khashoggi — by then one of Saudi Arabia’s most prominent dissidents — startled the staff at the Saudi Consulate in Istanbul by visiting to obtain a certificate of marriage eligibility.   

“We were all shocked,” the consulate’s security attache said in a phone call to an official in Saudi Arabia on Sept. 28, the day of Khashoggi’s first visit last year. “It is known that he is one of the people sought.”

The details, and other revelations in the report, ended a respite for Saudi officials from international censure as the killing faded from conversations among allies and investors. Instead, the focus had turned to Iran, with Saudi Arabia positioned as vital to countering security threats attributed to Tehran.

Callamard, a special rapporteur for the Office of the U.N. High Commissioner for Human Rights, said that Saudi authorities participated in the destruction of evidence after Khashoggi was killed and that culpability for the slaying extends beyond the 11 Saudis who are on trial in a closed-door judicial proceeding in the kingdom.

“Mr. Khashoggi’s killing constituted an extrajudicial killing for which the State of the Kingdom of Saudi Arabia is responsible,” Callamard’s report said.

Adel al-Jubeir, the kingdom’s minister of state for foreign affairs, dismissed the findings in posts on Twitter on Wednesday. He said the report included “contradictions and baseless allegations.”

Jubeir also rejected the report’s calls for a U.N.-assisted criminal inquiry into the killing, saying that the “judicial authorities in the kingdom are the only ones competent to hear this case.”

Callamard said she found no “smoking gun” incriminating the crown prince himself but said he had played an essential role in repressing dissidents and almost certainly knew that a criminal mission targeting Khashoggi was being planned. 

“Evidence points to the 15-person mission to execute Mr. Khashoggi requiring significant government coordination, resources and finances,” she wrote. “While the Saudi government claims that these resources were put in place by Ahmed Asiri, 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 Mr. Khashoggi, was being launched.”

Asiri, Saudi Arabia’s former deputy head of intelligence, is one of two senior Saudi officials implicated by the kingdom’s prosecutors in the killing and the only senior official on trial.

Callamard’s account of Khashoggi’s death is the most definitive to date, even though her inquiry was hampered by Saudi Arabia’s refusal to allow her to visit the kingdom to conduct interviews. 

Secretary of State Mike Pompeo and President Trump have deplored the killing of Khashoggi, who was a contributing columnist for The Washington Post in the year before his death. But they have said the relationship with Saudi Arabia is too important to be sidetracked by a single incident.

Pompeo recently said the United States, invoking emergency powers because of rising tensions with Iran, will sell weapons worth $8 billion to Saudi Arabia and the United Arab Emirates.

At Wednesday’s Senate confirmation hearing for Kelly Knight Craft, Trump’s nominee to become U.S. ambassador to the United Nations, Sen. Lindsey O. Graham (R-S.C.) laid blame for Khashoggi’s slaying squarely on the Saudi crown prince.

“He did it,” said Graham, one of the biggest Republican critics of Trump’s approach to the kingdom. “Wouldn’t have happened without him, he knew it was going to happen, he wanted it to happen, he caused it to happen, and this is just the tip of the iceberg of other things going on in this kingdom.”

Human rights groups echoed Callamard’s call for an international investigation.

“Callamard’s report underscores that there will be no justice for Jamal Khashoggi unless Congress steps up,” said Rob Berschinski, the senior vice president for policy at Human Rights First. “Saudi leaders have made it clear that they intend to get away with murder. President Trump has made it clear that he values arms sales over the killing and dismemberment of a U.S. resident. Congress must make it clear that it will not let this stand.”

In a telephone interview from Geneva, Callamard characterized the U.S. response as ambiguous and conflicted.

“At the highest level of the U.S. government, there has not been a determination to hold to account the state of Saudi Arabia,” she said. She called U.S. sanctions against 17 suspects, most of them low- to mid-level personnel, insufficient.

Callamard offered a macabre account of Khashoggi’s final moments, drawn from audio recordings that captured events inside the consulate in the days before Khashoggi visited a second time and on the day of the killing. She said she was permitted to listen to 45 minutes of conversation — a small fraction of the seven hours of audio captured by Turkish intelligence. Her team was permitted to keep notes on only a portion of the recordings. Other conversations “were reconstructed from memory,” she wrote.

Some of the audio was hard to discern. “For instance, on the basis of recordings, the Special Rapporteur could not reach firm conclusions about what [she and her investigators] were told was the sound of a ‘saw’ in operation. The Turkish authorities undoubtedly have more information and intelligence about events in the Saudi Consulate than they were willing or able to share with the inquiry,” the report said.  

According to the report, 13 minutes before Khashoggi entered the consulate on Oct. 2, two of the Saudi agents, Maher Mutreb and Salah Tubaigy, a forensic expert, discussed dismembering the body.

“Joints will be separated,” Tubaigy told Mutreb. “First time I cut on the ground. If we take plastic bags and cut it into pieces, it will be finished.” Khashoggi’s name was not mentioned, but Mutreb referred to the “sacrificial animal.”

The report also said that Tubaigy “expressed concerns” about what was about to transpire, telling Mutreb: “My direct manager is not aware of what I am doing. There is no one to protect me.”

The audio suggests they attempted to make Khashoggi think he would be kidnapped and repatriated to Saudi Arabia, not killed.

When Khashoggi arrived at the consulate on Oct. 2, he was invited to the consul general’s office and asked whether he would return to Saudi Arabia.

“He responded that he wanted to return in the future,” the report states.

But the Saudi agents, using the pretext of an Interpol warrant, said they were there to take him back to the kingdom.

More conversation followed, the report said. Khashoggi insisted that people were waiting for him outside, as one of the agents tried to persuade him to send a message to his son. “What should I say?” Khashoggi asked. “See you soon? I can’t say kidnapping.”

“Type it Mr. Jamal,” one of the agents replied. “Hurry up. Help us so that we can help you because at the end we will take you back to Saudi Arabia and if you don’t help us you know what will happen at the end.”

Then, in the recordings, “sounds of a struggle can be heard,” the report said.

In her report, Callamard ­painted a poignant picture of Khashoggi. 

An important but traditionalist journalist in Saudi Arabia, Khashoggi “was not seen by dissidents to be naturally ‘one of them,’ ” Callamard wrote. Increasingly isolated by his views, he went into self-exile. Living in the Washington area, he had little income, little security and little status, making him lonely and unhappy, Callamard wrote. His decision to remarry suggested he was preparing to live a fuller, more settled life, she said.

Fahim reported from Istanbul. Karoun Demirjian contributed to this report.