What investigators choose to make public over the coming days - and how - depends on behind-the-scenes negotiations between Ankara and Riyadh, whose already fragile relationship is being sorely tested.
"We would like to know exactly what happened inside the Saudi Consulate in Istanbul and the circumstances surrounding his disappearance", said Mohamed Okad, a friend of Khashoggi and founder of Insight into Crisis, a conflict advisory group.
The Khashoggi case puts the Trump administration unexpectedly on the side of Turkey, where two top government officials have been slapped with United States sanctions over the detention of an American pastor.
She told journalists that he had been required to surrender his mobile phone to consulate staff, and Khashoggi had advised her to call an adviser to the Turkish President, if he failed to emerge. He said he was personally following the case and would announce the results of the investigation at an undisclosed time.
Turkey has demanded answers about what happened to the exile in the building, and the government has summoned the Saudi ambassador twice to get them. "I would like to confirm that.Jamal is not at the consulate nor in the Kingdom of Saudi Arabia, and the consulate and the embassy are working to search for him", the consul-general, Mohammed al-Otaibi, was quoted as saying.
Khashoggi's disappearance could put pressure on the Saudi crown prince, who has promoted an image of himself as a reformer and a reliable Western ally.
Khashoggi had been close to the previous Saudi regime, but fled the kingdom a year ago, soon after the new monarch anointed his son, MBS, as prince.
Khashoggi had gone to the consulate to receive an official document for their marriage.
Trump Threatens to Cut Aid to Central American Nations Over Migrant Caravan
Trump has repeatedly claimed the Democrats don't care about security or law and order, particularly when it comes to immigration . Central American migrants walking to the United States start their day departing Ciudad Hidalgo, Mexico, Oct. 21, 2018.
Turkish officials have said they believe Khashoggi, 59, a critic of the Saudi leadership and a contributor to the Washington Post's Global Opinions section, was killed by a team of 15 Saudis flown in specifically to carry out the attack.
Khashoggi had written a series of columns for the Post that were critical of Saudi Arabia's assertive Prince Mohammed, who has led a widely publicized drive to reform the conservative Sunni monarchy but has also presided over the arrests of activists and businessmen. Saudi officials maintain he left the consulate shortly after entering, though it has failed to provide evidence to back that up, such as video footage. The private Turkish broadcaster NTV reported Monday that police had requested access to the Saudi Consulate.
Saudi national Mr Khashoggi, 59, who had been living in the USA for a year, condemned the regime over arrests of activists and the war in Yemen.
"And the Turkish government must assume its role and deal with the case of Jamal Khashoggi because Turkish sovereignty has been violated", she added. "Saudi Arabia must return to supporting the Syrian revolution and partnering with Turkey on this".
Reuters news agency is given a tour of the six-storey Saudi consulate to prove that the missing journalist is not being detained there.
CNN reported Sunday that the United States government is quietly working Khashoggi's case across several agencies and at senior levels of the administration.
"Obviously it is very challenging for the Turks because they enjoy strong diplomatic relations with the Saudis, which is one of the reasons they did not comment immediately following the disappearance of Khashoggi", Elshayyal added.
The Saudi government vehemently denied those reports.