Turkey has since demanded the extradiction of the 18 officials accused of Khashoggi's murder.
Mr Trump and Prince Mohammed have cultivated warm ties, though the US President said earlier last week that the Crown Prince, as the kingdom's de facto ruler, bore ultimate responsibility for the operation against Mr Khashoggi.
He continued that the failure of any nation to adhere to worldwide norms and the rule of law undermines regional stability at a time when it is needed the most, falling short of taking aim at the Crown Prince Mohamed bin Salman.
Media captionJamal Khashoggi: What we know about the journalist's disappearance and death What else did his fiancée say?
On Thursday, CIA Director Gina Haspel briefed Trump about her recent trip to Turkey, where she listened to purported audio of Khashoggi's killing.
Cengiz, who is studying for a PhD in Istanbul, also said she declined an invitation to the USA from President Donald Trump, a staunch defender of the Gulf kingdom.
Erdogan and Trudeau stressed the need to shed light on the killing and the importance of punishing the culprits, said a source from Turkish presidency, who asked not to be named due to restrictions on speaking to the media.
Cengiz said Khashoggi was concerned tensions would arise when he visited the consulate for the first time on September 28, but he was treated well at that visit, which appeared to reassure him, she said.
"We never questioned the wisdom of Oman's Sultan Qaboos to contribute to Israel-Palestine issue and we wish him well in his effort", Sheikh Khalid bin Ahmed said.
Meanwhile, the crown prince has been assigned by his father, King Salman, to oversee the restructuring of Saudi intelligence bodies in the aftermath of the killing.
Hatice Cengiz, who is Turkish, also said in an interview on Turkish television channel HaberTurk on Friday that she continually asks herself questions about October 2, the day that Khashoggi entered the consulate and was killed by officials there.
While these were some of the sharpest comments Mattis has made on the Khashoggi killing, he also said the two countries still needed to collaborate on stability in the region.
Germany and Saudi Arabia only returned their ambassadors in September after 10 months of frosty relations following criticism from Berlin of what it said was Saudi interference in Lebanese affairs.
Saudi Arabia is the lynchpin of a USA -backed regional bloc against Iran but the crisis has strained Riyadh's relations with the West. Dozens of Western officials, bankers and executives shunned a big investment conference in Riyadh this week.