WHEN TURKISH authorities first told reporters last Saturday that journalist Jamal Khashoggi had been murdered inside Saudi Arabia’s consulate in Istanbul, they offered few details and no evidence to back up the sensational claim. To the credit of the government of Recep Tayyip Erdogan, that has now changed.

The Post has obtained video recordings and other evidence showing how a group of 15 Saudi operatives entered the country on Oct. 2, the day Mr. Khashoggi visited the consulate. The private-plane flights the Saudis took from Riyadh have been documented, along with the Saudis’ movements around Istanbul. Their names and photographs have been published in a Turkish newspaper. According to Reuters, which reviewed social and Saudi media, one is a forensic scientist, while others are military officers.

Official Turkish sources said the men are believed to have killed Mr. Khashoggi and transported his body out of the consulate. The officials have described more evidence that has not yet been publicly released: One of our sources says the Turks possess an audio recording of the murder. U.S. officials have been briefed on the evidence, and The Post reports that U.S. intelligence intercepts revealed that Saudi Arabia’s de facto ruler, Crown Prince Mohammed bin Salman, ordered an operation to lure Mr. Khashoggi back to the kingdom from Washington, where he has been living in self-imposed exile and contributing commentaries to The Post.

The publicly available evidence is not entirely conclusive. But it clearly shows that Saudi officials, including the ambassador in Washington, were not telling the truth when they denied the existence of the Saudi team. The Saudis have been saying that Mr. Khashoggi left the consulate shortly after arriving, and that they have no knowledge of what happened to him; the ambassador to the United States, Khalid bin Salman, even professes to share the concerns about Mr. Khashoggi’s welfare. That cynical stance has been shredded. As Sen. Tim Kaine (D-Va.) told us on Wednesday, “The burden of proof is now on the Saudis” to show they were not responsible for Mr. Khashoggi’s disappearance.

In the absence of an adequate response, the regime must be held responsible. As Mr. Kaine rightly put it, “We will have to analyze everything about the U.S.-Saudi relationship,” including military sales and cooperation.

The crown prince is not the only one who needs a new response to the Khashoggi case. Until Wednesday, President Trump, who has treated the Saudi ruler more favorably than the leaders of Canada and Germany, professed not to know what might have happened to the journalist. On Wednesday, he said, “It’s a very serious situation for us and this White House. . . . I think we’ll get to the bottom of it.”

That’s better than claiming ignorance, but it is still a tepid reaction. Mr. Trump ought to consult his own intelligence officials and diplomats, who are well informed about the evidence. He should accept that a regime that is vicious and reckless enough to oversee the killing of a journalist in a diplomatic facility, then blatantly lie about it, cannot be a trustworthy partner of the United States. If the crown prince’s government does not immediately explain what happened to Mr. Khashoggi, and punish those responsible, it must be punished with sanctions — by Congress, if Mr. Trump cannot bring himself to act.