ISTANBUL -- The Turkish fiancee of slain journalist Jamal Khashoggi has called on U.S. President Donald Trump and other leaders to ensure that his death in Istanbul is not covered up, while Saudi Arabia's top prosecutor on Tuesday visited the Saudi Consulate where officials from his government killed the writer.

Speaking at a memorial in London on Monday, Hatice Cengiz expressed disappointment in the "leadership of many countries." Singling out Trump, she urged him to "help reveal the truth and ensure justice be served."

"He should not pave the way for a coverup of my fiance's murder. Let's not let money taint our conscience and compromise our values," she said.

Cengiz also told the memorial that she wishes she had entered the consulate instead of Khashoggi, a Washington Post columnist who had written critically of Saudi Arabia's crown prince.

Khashoggi vanished after entering the consulate in Istanbul on Oct. 2 to pick up paperwork for his upcoming marriage with Cengiz, who was waiting for him outside.

Turkey alleges a Saudi hit squad from Saudi Arabia travelled to Istanbul to kill the journalist and then tried to cover it up. Under mounting pressure, Saudi Arabia changed its narrative about Khashoggi's killing several times, eventually admitting that Khashoggi died inside the consulate and only recently acknowledging that Turkish evidence shows his killing was premeditated.

In an interview with ABC News, Cengiz said Khashoggi had been worried about being spirited back to Saudi Arabia the first time he went to the consulate unannounced on Sept. 28, but was pleasantly surprised when he received a warm reception.

"Naturally, after the first positive visit we had no reasons to think that there would be any sort of danger," Cengiz told ABC. "Our second visit was full of hope and it was the last step to our union."

She said during the memorial: "If only I knew that would be the last time I would see my Jamal, his smile, hear his laughter, I would have stood in front of that murderous team myself."

Cengiz last week declined an invitation by the White House, criticizing Trump's statements on Khashoggi's killing.

Saudi Arabia's top prosecutor, Saud al-Mojeb, arrived at Istanbul's main courthouse Tuesday for more talks with Istanbul's chief public prosecutor, Irfan Fidan, on the investigation into the killing, Turkey's state-run Anadolu Agency reported. The two had met for an hour and 15 minutes on Monday as part of an agreement between Riyadh and Ankara for co-operation over the investigation.

Al-Mojeb then went to the consulate and left after spending a little over an hour there.

Turkish President Recep Tayyip Erdogan said the investigation needs to be completed swiftly.

"This needs to be solved now; there is no point in excuses," Erdogan told journalists.

Erdogan said the prosecutor repeated to his Saudi counterpart Turkey's extradition request for 18 suspects detained in Saudi Arabia for the killing to be put on trial in Istanbul. Fidan asked al-Mojeb to reveal who sent this group, according to the president.

The country is also asking Saudi Arabia to help locate Khashoggi's body, which still has not been found. Erdogan said Riyadh must disclose the identity of an alleged local collaborator said to have been involved in disposing Khashoggi's body.

The U.N. human rights chief, Michelle Bachelet, also urged Saudi Arabia to reveal the location of the writer's remains.

In her strongest public comments yet on the subject, she said international experts should have complete access to evidence and witnesses.

She added: "I urge the Saudi authorities to reveal the whereabouts of his body without further delay or prevarication."

Saudi Foreign Minister Adel al-Jubeir has said the kingdom will try the perpetrators and bring them to justice after the investigation is completed.

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Fraser reported from Ankara, Turkey. Mehmet Guzel in Istanbul contributed.