"The Turks don't trust any diplomats and they have been into most embassies and most consulates in Turkey and they listen to what's going on -- and if indeed there are tapes proving that he was murdered, I think that's probably how they know. But the Turks are very reluctant to admit that."
https://www.cnn.com/2018/10/12/middleeast/khashoggi-saudi-turkey-recordings-intl/index.html