After Saudi journalist Jamal Khashoggi vanished inside the Saudi Arabian consulate in Istanbul almost a year ago, his fiancée became a familiar figure around the world, an anxious woman in a headscarf pleading for answers about his fate.

But Khashoggi was never seen alive again. Hatice Cengiz eventually learned he had been slain inside the consulate by fellow Saudis, who had waited in ambush. The CIA and other foreign intelligence agencies concluded that Saudi Crown Prince Mohammed bin Salman ordered the killing of Khashoggi, a Washington Post columnist who had dared to openly criticize the de facto ruler of the Saudi kingdom.

With the first anniversary of the death approaching on Oct. 2, Cengiz came to New York — where heads of state gathered for the United Nations General Assembly — to demand accountability for Saudi Arabia, which she said has never had to face serious consequences over the case.

"His fellow journalists did their best that so no one could push this under the carpet," she told NBC News in an interview. "Saudi Arabia was put under massive pressure, thanks to international media coverage."

"But at the end of the day, all of these efforts did not persuade world leaders to sanction Saudi Arabia. That is so sad," she said.

"There was a lack of reaction in the E.U. and in the United States. This should have been a lesson to Saudi Arabia that they can and should also be held accountable."

Jamal Khashoggi at a press conference in the Bahraini capital, Manama. Mohammed Al-Shaikh / AFP - Getty Images file

Her comments came as the crown prince broke his silence and spoke for the first time about his role in the killing.

"It happened under my watch," he told PBS' "Frontline." "I get all the responsibility, because it happened under my watch."

But he said the murder was carried out without his knowledge.

Cengiz spoke to NBC News in a hotel room near the U.N. headquarters in Manhattan, where Saudi leaders this week were conferring with U.S. and other officials on tensions with Iran and the war in Yemen. President Donald Trump did not mention the Khashoggi case in his public statements.

Cengiz was joined in New York by others whose loved ones have also run afoul of the Saudi government: Lina al-Hathloul, sister of detained Saudi women's rights activist Loujain al-Hathloul, and Abdullah Alaoudh, son of imprisoned Saudi Islamic scholar Salman al-Awdah, who faces a death sentence.

Cengiz has demanded a full accounting of Khashoggi's death and the recovery of his remains.

Cengiz, who had met Khashoggi in May last year, said the international attention triggered by his killing meant she felt the full weight of her loss only months later.

"It took me a long time to enter into mourning," she said.

She said she found herself swept up in the aftermath of a "political assassination" with international implications, and her phone ringing around the clock. "I wasn't prepared for such a situation. I was just an ordinary, simple research assistant doing post-graduate studies. I couldn't mourn properly."

But finally, the tragedy sank in, she said. "After a long delay, I experienced this huge shock wave."

Cengiz, a Turkish national, said she has moved to London to distance herself from the "scene of the crime" in Istanbul, and to learn English. But she said she recognizes that there is no escaping the horror that took place.

"For the rest of my life, Jamal's murder will be an agony."

Khashoggi, who had opted to live in exile as a U.S. resident in Virginia to write freely without risk of imprisonment, disappeared after entering the Saudi consulate Oct. 2, 2018.

Saudi officials initially denied Khashoggi's death before acknowledging he was the victim of a premeditated killing. But the government has insisted the crown prince was not behind the killing and says 11 suspects are being tried in connection with the case.

A special U.N. investigator in June said in a detailed report that the crown prince should be investigated for the crime and that there is "credible evidence" that he and other senior officials are liable for the killing of Khashoggi.

The U.N. special rapporteur found that Khashoggi was "the victim of a deliberate, premeditated execution, an extrajudicial killing for which the state of Saudi Arabia is responsible under international human rights law."

Saudi officials have dismissed the U.N. report.

Trump has expressed doubts about the crown prince's role and said the U.S. needs to preserve its alliance with the Saudis, particularly because Riyadh is a major customer for American military hardware.

Cengiz said Khashoggi did not see himself as a sworn enemy of his native country, having served earlier in his life as an adviser to members of the royal family and to government officials. Instead, he intended his commentaries to be taken as constructive but not hostile criticism, she said.

His vision for Saudi Arabia was not to tear down the House of Saud, but to reform it into a constitutional monarchy with a democratically elected parliament, she said.

Members of the royal family and government officials often called him to "give him feedback" about his columns, she said. "He always had a relationship with the Saudi government and royal family."

As a result, Khashoggi did not fear for his life, even if he did take precautions not to travel to other Arab countries or agree to appointments with strangers, according to Cengiz.

"He thought no one would bother him abroad. No one warned him or threatened him," she said.

Khashoggi, however, had become increasingly concerned about the growing power of the crown prince, she said. He believed the crown prince was breaking with Saudi tradition by targeting intellectuals and journalists and taking major decisions without consulting widely beforehand, she said.

"What Jamal was hoping for was real, deep-rooted change in the country," she said, "and Jamal thought such a chance could not depend on one person only."

Saudi Arabia did not respond to a request for comment.