Turkey's ability to investigate this murder though was "seriously curtailed and undermined by Saudi Arabia's unwillingness, for some 13 days, to allow Turkish investigators access to the crime scenes".
Trump has resisted efforts in the US Congress to rebuke the Saudis, pointing to weapons sales as an important source of US jobs.
When al-Qahtani, who US intelligence says was the ringleader of the murder, warned the prince that targeting Khashoggi could create an global uproar, he was told Saudi Arabia should not care about worldwide reaction to how it deals with its own citizens.
The conversation, which was intercepted and transcribed by the USA intelligence, took place during the period when Riyadh's concerns about Khashoggi's criticism were growing and amid the prince's moves to tighten his grip on power in Saudi Arabia, the newspaper noted.
She said that Saudi killers had exploited diplomatic immunity to carry out the murder.
According to the WSJ, the CIA's assessment was not hinged on a "smoking gun" but rather on a deep "understanding of how Saudi Arabia works", said officials familiar with the intelligence agency's conclusion.
The WhatsApp messages between MBS and Qahtani, who is believed to have overseen the team that killed Khashoggi in the Saudi consulate in Istanbul, was one piece of evidence cited in the Central Intelligence Agency assessment. "Our leadership is a red line".
USA intelligence agencies had previously concluded that the crown prince must have at least had knowledge of the plot, leading some members of Congress to call for him to step down as the de facto leader of the country.
Trump has publicly said that he is not concerned whether Prince Mohammed was involved, saying the Saudi alliance benefits Washington due to the kingdom's major purchases of weapons and its hostility to regional rival Iran.
Special UN rapporteur Agnes Callamard said on Thursday after a visit to Turkey that the killing of Khashoggi, who had written critical pieces on Saudi Arabia in the Washington Post, had been "planned and perpetrated" by Saudi officials.
"I wish the Congress would take a step back, look at the overall relationship, look at the steps that Saudi Arabia has taken, and let the process play out", he added.
Altun said Turkey's findings on the case were in line with those of the UN-led inquiry, adding that Ankara was committed to cooperating in a potential United Nations investigation into the case.
However she denounced the fact that Khashoggi's remains still had not been found.
Khashoggi's killing has severely strained ties between Turkey and Saudi Arabia, although Erdogan has good ties with the Saudi monarch, King Salman.