Cengiz said her fiancee's death had left a "void" in her life and had turned him into a "martyr" for the cause of democracy in Saudi Arabia.
U.S. President Donald Trump has said he wants to get to the bottom of the case, while also highlighting Riyadh's role as an ally against Tehran and Islamist militants, as well as a major purchaser of U.S. arms.
Khashoggi, who had fled the kingdom recently and taken up residency in the United States, entered the Saudi Consulate in Istanbul on October 2 to retrieve paperwork that he needed to marry his Turkish fiancée.
Ms Cengiz, who was waiting outside, raised the alarm after her fiancé didn't reappear after ten hours.
Al-Mojeb, the prosecutor visiting Istanbul, was named attorney general by Saudi King Salman a year ago after a palace shakeup that saw Prince Mohammed sideline his elder, more experienced cousin, Mohammed bin Nayef, for the title of crown prince.
Speaking later on Sunday at a joint news conference in Prague with Czech Prime Minister Andrej Babis, Mattis was asked how an investigation would be able to determine whether Saudi Arabia's powerful Crown Prince Mohammed bin Salman had any involvement in the killing.
Turkish prosecutors have prepared a request for the extradition from Saudi Arabia of 18 suspects who were arrested by Riyadh as part of the investigation.
"President Trump should help reveal the truth and ensure justice be served".
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The country is the final stop for the royals who are on a 16-day tour which has seen them also visit Australia, Fiji and Tonga . Add Royal Family as an interest to stay up to date on the latest Royal Family news, video, and analysis from ABC News.
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Social media posts by someone with the name Robert Bowers were also reported to be full of anti-Semitic comments. HIAS is a Maryland-based non-profit group that helps refugees around the world find safety and freedom.
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Ronald Lowy, a Miami attorney, said Sayoc showed no ability at the time to back up his threat with any bomb-making expertise. Two businesses are listed at the 375 Greenwich St. address: the Tribeca Film Festival, and the Tribeca Grill .
While there have been recent unsubstantiated claims in Iran that Saudi Arabia has been supplying ingredients that can be used to produce the nerve agent Sarin in Yemen, it is more likely that Mr Khashoggi was referring to phospherous.
"If only I knew that would be the last time i would see my Jamal, I would have stood in front of that murderous team myself".
He clarified later that the murder and cover-up should have never happened.
"We discussed it. You know the same thing we talked about, the need for transparency, full and complete investigation", Mattis told a small group of reporters traveling to Prague with him. "Jamal was my beloved fiancée, but he was also a gentle human being, a loving man, a journalist and a true believer in democracy and freedom in the Arab world", she said. "Let's not let money taint our conscience and compromise our values", she told a memorial in London for the slain Washington Post columnist.
Trump has hedged his criticism of Saudi leaders over Khashoggi, insisting he does not want to imperil a "tremendous order" of US$110 billion (RM459.75 billion) of weapons he says will support 500,000 United States jobs - figures that experts say are highly exaggerated. But the decision to marry in Istanbul, whose mosques reminded Mr. Khashoggi of his hometown Medina, set off a paper chase that ultimately ended in death.
Turkish law required that Khashoggi, who was divorced, provide proof that he did not have a wife and thus his trip to the consulate.
He said Turkey is in "intense" efforts to reveal all the names behind the incident, while adding that the "body of Khashoggi couldn't be reached yet". Jim Inhofe, R-Tulsa, who is chairman of the Senate Armed Services Committee.