Turkish media close to the president published images Wednesday of what it described as a 15-member "assassination squad" allegedly sent to target Saudi journalist Jamal Khashoggi, and of a black van later travelling from the Saudi consulate, where he went missing, to the consul's home.
"Two possibilities, either he was killed at the consulate and his body transported out on to the planes onward to Dubai/Cairo - then Riyadh, or he was abducted at the consulate and renditioned back to Saudi Arabia", a Turkish security official told TRT.
The Sabah newspaper published images of the men apparently taken at passport control. It said they checked into two hotels in Istanbul on October 2 and left later that day.
Officials in Saudi Arabia did not immediately respond to a request for comment.
Stills of the airport show the men arrived from Riyadh to Istanbul in two private jets with the tail numbers HZ SK1 and HZ SK2, the Daily Sabah reported.More news: Apple fixes iPhone XS charging problems (and more) in iOS 12.0.1
A columnist with the Washington Post, Khashoggi was living between Washington DC and Istanbul at the time of his disappearance, and was visiting the consulate in order to obtain documents proving an earlier divorce so that he could marry his Turkish fiancée.
"In most cases, their arrests have never been officially confirmed and no official has ever said where they are being held or what they are charged with", said the watchdog.
A week after the disappearance of Saudi dissident journalist Jamal Khashoggi, details about what happened to him at the Saudi consulate are beginning to emerge, along with indications that the USA had information of a Saudi plot against him.
The next day, according to Turkish security officials, both traveled to the Saudi capital, Riyadh.
Saudi Arabia is a major investor in Turkey, despite Ankara's support for the Gulf nation of Qatar, which is under a blockade led by Saudi Arabia and three other Arab nations.
Khashoggi, a Washington Post contributor who has written columns critical of the kingdom's powerful Crown Prince Mohammed bin Salman, went missing on October 2 after entering the consulate for paperwork needed to marry his Turkish fiancée.More news: Star Trek: Discovery season 2 trailer reveals the new Spock
On Wednesday, the Post published a column by Khashoggi's fiancee, Hatice Cengiz.
Turkey's Hurriyet newspaper and other media alleged Wednesday that the Saudi Consulate's 28 local staff were given leave on October 2 on grounds that a "diplomats' meeting" would be held there on that day.
An unnamed senior official told the New York Times there was a complex operation in which Mr Khashoggi was killed within two hours of arriving and then dismembered. Fifteen people reportedly traveled to Istanbul aboard two charter flights, including one person who is believed to be an autopsy expert that may have helped dismember Khashoggi's body to remove it from the building.
Before Khashoggi disappeared, U.S. intelligence intercepted communications of Saudi officials discussing a plan to grab him, the Washington Post reported.
Trump, who took his first overseas trip as US President to the kingdom and whose son-in-law Jared Kushner has close ties to Prince Mohammed, said Tuesday he had not yet talked to the Saudis about Khashoggi, "but I will be at some point", without elaborating.
The country's foreign ministry has said it is "open to co-operation" and a search of the building can go ahead as part of the investigation.More news: The American Music Awards 2018