Turkish investigators were studying DNA samples on Wednesday as they probed the case of Jamal Khashoggi, amid growing indications that the men allegedly responsible for the Saudi journalist's disappearance have close ties to the highest levels of the Saudi government.

Sources told CNN that a group of Saudi men whom Turkish officials believe are connected to Jamal Khashoggi's possible death were led by a high-ranking intelligence officer, with one source saying he was close to the inner circle of the kingdom's Crown Prince Mohammed bin Salman.

Khashoggi, a Washington Post columnist, visited the Saudi consulate in Istanbul on October 2 to obtain papers that would have allowed him to marry his Turkish fiancée. The insider-turned-critic of the Saudi government has not been seen since.

Turkish officials have told CNN that Khashoggi's body was dismembered after he was killed in the consulate.

Investigators were examining “a large number of DNA cell samples” collected during searches on Monday of the Saudi consulate building and its sewers, Turkish state news agency Anadolu reported on Wednesday.

Turkish officials have not yet searched the Saudi consul general's residence in Istanbul.

US Secretary of State Mike Pompeo visited Saudi Arabia on Tuesday where he held talks with King Salman and Crown Prince Mohammed bin Salman, who he said “strongly denied” any knowledge of what happened to Khashoggi.

Sources have told CNN that the kingdom was preparing a report to acknowledge that Khashoggi died at the consulate in Istanbul in an interrogation that went awry. One source said the report will likely conclude that the operation was carried out without clearance and transparency and that those involved will be held responsible.

But a Saudi admission that Khashoggi died in the consulate would not deter difficult questions over the whereabouts of his remains or the movements of the 15 men and their links to bin Salman.

Questions have also been raised by Turkish authorities over Saudi Arabia's lack of cooperation in investigating the disappearance.

By the time Turkish investigators gained access to the consulate Monday evening, a fresh coat of paint had been applied “everywhere” inside the building, a Turkish official told CNN on Tuesday. The source demanded that Saudi Arabia make “a genuine contribution” to the investigation.

Previously, a source familiar with the ongoing investigation told CNN that Turkish authorities have audio and visual evidence that showed Khashoggi was killed inside the Saudi consulate. The evidence, which was described to the source by a Western intelligence agency, showed there had been an assault and a struggle inside the consulate, along with the moment Khashoggi was killed, the source said.

US President Donald Trump defended Saudi Arabia in an interview on Tuesday, suggesting that the wave of criticism the Middle Eastern kingdom has faced over Khashoggi's disappearance was premature.

Trump has been reluctant to castigate the kingdom, a key US ally, despite growing pressure at home and internationally. His recent comments may be a sign that Washington is preparing to accept Saudi Arabia's efforts to distance its leaders from whatever fate befell Khashoggi.