According to Turkish authorities, based on the evidence Saudi operatives had tortured, murdered, and dismembered Khashoggi at the monarchy's consulate in Istanbul.
The announcement underscored the rapidly mounting pressures on Saudi Arabia to fully illuminate Khashoggi's killing, after its previous explanations were contradicted by Turkey and met with skepticism by the United States, a close Saudi ally.
Riyadh finally accepted on Thursday what Turkey had said virtually from the start - that he was killed in a premeditated hit. US intelligence officials and lawmakers as well as the European Union have said that an operation targeting a critic of the royal court in a foreign country is unlikely to have been ordered without the knowledge of senior Saudi officials.
Pro-government Turkish newspaper Yeni Safak, citing the audio, has said his torturers cut off his fingers during an interrogation and later beheaded him. It was not clear what could be heard. "Where is it?" Turkish Foreign Minister Mevlut Cavusoglu said at a news conference with his Palestinian counterpart.
Turkey said it believed a hit squad of Saudi nationals had travelled to Istanbul with the sole goal of killing Khashoggi, a former member of the Saudi elite who became critical of the current government's administration in his country. "(Saudis said) "Let's give a lesson to him".
Also Thursday, the European Union issued a fresh condemnation of Khashoggi's killing and reiterated its skepticism that it could have been carried out without Mohammed's knowledge.
"It is tragic that it took his death to get the Saudi authorities to grant them the freedom to travel", Slim told AFP.
Saudi Arabia has detained 18 people and dismissed five senior government officials as part of the investigation into Khashoggi's murder.
Turkish police were investigating water samples from a well at the consulate on Thursday after initially being denied access, broadcaster CNN Turk said.
Ilnur Cevik, an adviser to Turkish President Recep Tayyip Erdogan has accused Saudi Crown Prince Mohammed bin Salman of having Khashoggi's "blood on his hands".
"From this place where Jamal lost his life, we clearly state that we will not accept compromises in the case of his murder", said a statement from the group, read by Ayman Nour, the Egyptian chief of opposition broadcaster El-Sharq.
The prince promised on Wednesday the killers would be brought to justice, his first public comments on the matter.
The son of murdered Saudi journalist Jamal Khashoggi, Salah, and his family have left the Gulf kingdom after the government lifted a travel ban, Human Rights Watch said Thursday.
The U.S. State Department later confirmed that Salah Khashoggi was on his way to the U.S.
This week he held a meeting at the al Yamama Palace in Riyadh in which he and other family members received condolences from King Salman and the crown prince.