A second jet, with registration HZ-SK2, carried another batch of the 15 suspects, but was searched as by then the alarm had been raised that they might be behind Khashoggi's disappearance.
He reiterated Chancellor Angela Merkel's statement from Sunday, saying Berlin "at this stage will not approve further arms exports because we want to know what happened", adding that "all explanations so far have been unsatisfactory".
Saudi Arabia said 18 Saudis were arrested and that several top intelligence officials were fired.
The employee said the prosecutors asked them whether anything unusual happened on October 2 in the consulate, whether they had seen Khashoggi and the 15 other Saudis, how long they have been employed at the consulate and the working hours of the staff.
"Khashoggi was detained by the Saudi team inside the consulate building".
Trump has repeatedly said over the last week that he opposes any effort to impede more than $100 billion in US arms sales to Saudi Arabia, but that he would consider sanctions on the kingdom. After weeks of denying knowledge of his fate, Saudi officials said Saturday the prominent journalist was killed in a "rogue operation".
The White House said late on Sunday that US President Donald Trump had spoken to French President Emmanuel Macron and the two had discussed a range of issues including circumstances surrounding Khashoggi's death.
Trump chose Saudi Arabia as his first overseas trip as president, and his son-in-law and adviser Jared Kushner has developed close ties with Prince Mohammed, apparently seeing him as an ally in advancing his yet-to-be-released peace plan for Israel and the Palestinians.
A leading Republican US senator said he believed the crown prince was behind the killing, adding that the Saudis had lost all credibility in their explanations of his death.
CNN has obtained exclusive law enforcement surveillance footage, part of the Turkish government's investigation, that appears to show the man leaving the consulate by the back door, wearing Khashoggi's clothes, a fake beard, and glasses.
U.S. President Donald Trump had also talked about possible punishment but said he didn't want to halt a proposed $110 billion United States arms sale to Saudi Arabia because, he maintained, it would harm U.S. manufacturers.
"Khashoggi's clothes were probably still warm when Madani put them on", the official said. South Carolina Sen. Lindsey Graham said Sunday "I find it impossible to believe that the Crown Prince was not involved".
During a joint interview with Britain and France, Mrs Merkel said that she condemned the killing of Mr Khashoggi "in the strongest terms".
The report by pro-Government daily Yeni Safak alleges the Crown Prince telephoned the Washington Post columnist moments before he was killed in the Saudi consulate in Istanbul earlier this month. They said the "hypotheses" proposed so far in the Saudi investigation need to be backed by facts to be considered credible.
President Donald Trump says he needs to learn more about the killing of a Saudi journalist and will be working with Congress on the USA response.