One Turkish official said police would release evidence on Sunday to support their assessment that the journalist, Jamal Khashoggi, is dead.
Reacting to the news of his alleged murder, Mr Khashoggi's Turkish fiancee, Hatice Cengiz, said she "did not believe he has been killed". Another said it was a "high possibility". Both spoke on the condition of anonymity to discuss the ongoing investigation.
Rights groups have called on Saudi Arabia to verify Khashoggi's whereabouts, with Human Rights Watch calling on Turkey to deepen its investigation into the case, saying if Saudi Arabia had detained Khashoggi without acknowledging it, his detention would constitute an enforced disappearance.
Turkey's foreign ministry on Wednesday summoned Saudi Arabia's ambassador over Mr Khashoggi.
"If the reports of Jamal's murder are true, it is a monstrous and unfathomable act", Fred Hiatt, the director of The Post's editorial page, said in a statement.
Saudi Arabia's consul-general in Istanbul, Mohammad Al Otaibi, gave reporters a tour of the consulate to prove that the premises are clear and that the talk of kidnapping "is baseless".
Saudi Crown Prince Mohammed bin Salman has brushed aside United States President Donald Trump's warning that the oil-rich kingdom's leadership might not last "two weeks" without American military support, saying that his country existed decades before the USA.
According to his fiancee Cengiz, Khashoggi had visited the consulate to receive an official document for his marriage.
It said a team of Saudi investigators were in Turkey working with local authorities. "Jamal was - or, as we hope, is - a committed, courageous journalist".
Pompeo to visit Pyongyang for weekend talks with North Korean leader
That left Seoul lobbying hard for a second summit between Trump and Kim to keep alive a positive atmosphere for nuclear diplomacy. During their three-day stay, they will also tour major facilities and attend a mass gymnastics performance.
Have a cellphone? Expect a message from the feds this afternoon
ET on Wednesday, though FEMA says it might take a few minutes for the test to make it to all phones. On Wednesday, October 3, 2018, at 12:18 p.m. (MST) you'll receive a TEST text message.
Jokes and complaints as Trump sends 'presidential alert' to 225 million Americans
Did your phone alert you of a unusual message this afternoon? The wireless alert system launched in 2012. This will be the fourth nationwide test of the EAS after similar tests in 2011, 2016, and 2017.
"The idea of kidnapping of a Saudi citizen by a diplomatic mission is something that should not be [propagated] in the media" he said.
The journalist said he had been banned from writing in the pan-Arab Al-Hayat newspaper, owned by Saudi prince Khaled bin Sultan al-Saud, over his defence of the Muslim Brotherhood which Riyadh has blacklisted as a terrorist organisation.
And it's not restricted to Saudi Arabia.
Last week, Trump asked at a rally "when you have wealthy countries like Saudi Arabia, like Japan, like South Korea, why are we subsidising their military?"
Successive waves of arrests have targeted what the government said were corrupt businessmen, clerics plotting against the monarchy, and women's rights activists branded as traitors.
"I have left my home, my family and my job, and I am raising my voice", Khashoggi wrote in September 2017.
It's a theme he's been sounding for years, tweeting in March 2015 that if Saudi Arabia "wants our help and protection, they must pay dearly! I can speak when so many cannot".
The Washington Post contributor, 59, vanished after an appointment with Saudi officials on Tuesday.
Responding to his disappearance, the Washington Post earlier this week said it was "extremely concerned" about him.