SECRETARY OF STATE Mike Pompeo was said to be pressing in Riyadh on Tuesday for a “thorough, transparent and timely investigation” of the disappearance of the Saudi journalist Jamal Khashoggi. But the best metaphor for Mr. Pompeo’s diplomacy seemed to be what reporters witnessed outside the Saudi Consulate in Istanbul, where Mr. Khashoggi was last seen Oct. 2: the arrival of a cleaning crew with buckets, mops and fluids.

Mr. Pompeo, who smiled broadly as he greeted Crown Prince Mohammed bin Salman, appeared less intent on determining the truth than in helping the de facto Saudi ruler escape from the crisis he triggered. The Saudis are said to be preparing a cover story that will attribute Mr. Khashoggi’s murder to the excesses of a team that was dispatched to interrogate him. That would deflect blame from the crown prince, who in fact is believed to have ordered and overseen the operation.

President Trump signaled that he is more than ready to assist in that dodge. The president tweeted that in a phone call, the young Saudi leader had “totally denied any knowledge of what took place” — as if that should settle the matter. Mohammed bin Salman grandly declared to Mr. Pompeo, “We face our challenges together — the past, the day of, tomorrow.” “Absolutely,” the grinning U.S. envoy replied.

Back in Istanbul, the government of Turkish President Recep Tayyip Erdogan appeared more serious about trying to discover the truth. But its probe faced considerable obstacles: Mr. Erdogan told reporters that the investigators who were finally allowed into the consulate encountered freshly painted walls. Turkish sources told the Associated Press they have found more evidence backing up their claim that Mr. Khashoggi, a Post columnist and critic of Saudi rulers, was murdered and dismembered shortly after entering the compound. But the Turks, who put out word that they have an audiotape of the slaying, have made little of their evidence public. The longer they fail to provide full transparency, the more it will appear they are more concerned with what they can gain or lose from the affair.

All of this underlines the argument made in a Post op-ed by two senior U.N. officials: The only way to determine the truth about what happened to Mr. Khashoggi is to establish an independent international commission. “The Saudis cannot investigate themselves,” wrote David Kaye, the special rapporteur on freedom of expression, and Agnes Callamard, the special rapporteur on summary executions, adding that “the Saudi responsibility seems practically irrefutable.” Turkey, they said, should not head the investigation, because any inquiry that could lead to murder charges could be subverted by diplomatic pressure on Ankara.

Mr. Khashoggi’s family also has called for an independent investigation. The U.N. Security Council could launch such a probe by instructing the secretary-general to appoint a panel headed by a respected prosecutor or judge. Alternatively, the U.N. Human Rights Council could dispatch a mission. In either case, both Turkey and Saudi Arabia should be pushed to turn over the evidence they have, which could quickly establish what happened and who is responsible.

What should not be acceptable is a diplomatic cleanup operation conducted by the Trump administration for a regime and a ruler it has grossly indulged, despite its mounting excesses both at home and abroad. Until the full truth about Mr. Khashoggi is disclosed, U.S. businesses should shun the Saudi regime and Congress should block all military sales.