(CNN) A little over a week ago, a prominent Saudi journalist walked into the consulate general in Istanbul, intending to get paperwork that would allow him to marry his Turkish fiancée. She hasn't seen him since.

Since then, officials and journalists have scrambled to piece together the story of what happened to Jamal Khashoggi, a former Saudi royal insider who became a critic of the regime of Crown Prince Mohammed bin Salman.

Turkish authorities have privately said they believe Khashoggi was killed inside the consulate, a startling allegation that is firmly denied by the Saudis. Closed-circuit television footage, flight trackers, intercepted communications and even rumors of a bone saw have served as pieces of a puzzle that has spurred a diplomatic outcry.

In the latest developments on Wednesday, Turkish security officials concluded that the "highest levels of the royal court" in Saudi Arabia ordered the assassination of Khashoggi, according to a senior official cited by The New York Times

Turkish officials have said that a 15-person team flew from Saudi Arabia into Istanbul on the day Khashoggi entered the consulate, and they have provided information about two private planes that, they say, were involved in the transit of these Saudis. Aviation data analyzed by CNN backs up evidence of the planes' arrival in Istanbul.

The official quoted by the New York Times described the operation as "quick and complex," and that Khashoggi was killed within two hours of his arrival at the consulate. The agents "dismembered his body with a bone saw they brought for the purpose," the official told The New York Times. "It's like 'Pulp Fiction,'" he added.

About the only thing that is known for sure about Khashoggi's fate is that he was last seen at 1:14 p.m. local time last Tuesday as he entered the consulate.

His disappearance has prompted calls for investigations from around the world.

The kingdom's staunchest Western allies, including the United States, where Khashoggi had applied for permanent residency, have urged Saudi Arabia to come clean.

Trump said Wednesday that he's been in touch with the "highest levels" of the Saudi government about Khashoggi's case and expressed concerns about his possible murder. He said his administration was pressing the Saudi government to reveal more about the incident.

"We're demanding everything. We want to see what's going on here. It's a bad situation," Trump said in the Oval Office.

But he stopped short of saying whether he believed the Saudis have knowledge about his whereabouts, or may have played a role in his disappearance, stating that not enough was known to make a determination.

People hold posters of Saudi journalist Jamal Khashoggi during a protest organized by members of the Turkish-Arabic Media Association at the entrance to the Saudi Arabia Consulate on October 5, 2018 in Istanbul.

Khashoggi's fiancée, Hatice Cengiz, told CNN that although she is afraid that media reports of his death could be true, she wants to wait for a "final result" and still thinks "anything" could have happened to him.

A murder mystery?

Saudi Arabia has repeatedly denied Turkey's account of the story, saying that Khashoggi left the embassy on the same day he arrived.

In a statement to CNN on Wednesday, a Saudi official said the kingdom "categorically" denies "any involvement in Jamal's disappearance."

"At this stage, our priority is to support the investigation, as opposed to responding to evolving comments not directly related to those efforts. Jamal's well-being, as a Saudi citizen, is our utmost concern and we are focusing on the investigation as a means to reveal the truth behind his disappearance. Our sympathies go out to the family during this difficult time," the official said.

Timeline of Khashoggi's disappearance Tuesday, October 2 3:00 a.m.: One flight arrives in Istanbul from Riyadh 1:14 p.m.: Khashoggi arrives at the consulate 5:00 p.m.: Another flight arrives in Istanbul from Riyadh 6:00 p.m.: Second flight departs Istanbul for Cairo, en route to Riyadh 11:00 p.m.: First flight departs Istanbul for Riyadh Wednesday, October 3 Turkish officials first report Khashoggi is missing

But Turkish officials have repeatedly suggested that Khashoggi has been killed . A friend of the journalist, Turan Kislakci, who is also the head of the Turkish-Arab Media Association, told CNN that Turkish officials called him and "offered their condolences and told us to be ready for a funeral."

On Wednesday, a senior Turkish official speaking on the condition of anonymity told CNN that "the Saudis are not cooperating fully with the investigation. They are not open to cooperating."

In addition, Saudi authorities have asked Turkish authorities to postpone the search of their consulate in Istanbul, Turkey's pro-government daily Yeni Safak reported, citing anonymous security sources. The newspaper report did not mention a reason for the Saudis' request.

Saudi Arabia had earlier said it would allow Turkish authorities to search the consulate on the request of the Turkish Foreign Ministry, the newspaper said.

CNN reached out to the Saudi consulate in Istanbul by phone for comment. The person who answered the phone said that "the Saudi consulate does not have a comment" on the request for a delay, and hung up.

US officials are also attempting to piece together what happened, in particular whether any operation to silence Khashoggi was ordered at the highest levels of the Saudi government, including bin Salman.

One US official told CNN that the US is examining communications intercepts to see if it can learn any more about what may have happened.

US officials think it's possible the crown prince wanted Khashoggi silenced, but miscalculated the global impact his disappearance would have.

The Washington Post -- for which Khashoggi wrote critical columns -- said US intelligence intercepted communications of Saudi officials discussing a plan to capture the journalist. Citing a person familiar with the information, the Post said the Saudis wanted to lure Khashoggi back to Saudi Arabia and lay hands on him there.

It was not clear whether the Saudis intended to arrest and interrogate Khashoggi or to kill him, or if the United States warned Khashoggi that he was a target, the source told the Post.

CCTV cameras

CCTV footage in and around the premises of the consulate have emerged as a focal point of the inquiry into Khashoggi's fate.

CCTV image of Khashoggi entering the Saudi consulate on October 2.

A CCTV image obtained by CNN showed the missing Saudi journalist entering the Saudi consulate at lunchtime on October 2.

Cengiz waited outside, and says he never emerged. Turkish President Recep Tayyip Erdogan has demanded that the Saudis back up their claims that Khashoggi left the embassy alive by producing CCTV evidence. Such evidence has yet to emerge.

On Tuesday, The Guardian newspaper reported that the consulate's Turkish staff were told to take a day off the day Khashoggi disappeared. It also reported that Turkish investigators believe security footage from inside the consulate was removed and taken back to Saudi Arabia on a private jet.

During a tour of the six-story consulate given to journalists on Saturday, Saudi Consul General Mohammad al-Otaibi told Reuters that while the consulate was equipped with cameras, they did not record footage of Khashoggi entering or leaving the building.

A 15-man murder squad?

Turkish investigators have been focusing on the arrival of 15 Saudis in Istanbul last Tuesday. A Turkish police statement, quoted by state news agency Anadolu, said that the group of Saudis, who included several government officials, visited the consulate while Khashoggi was there.

Two executive jets belonging to a Riyadh-based company that does government contracting and corporate work were probably involved in ferrying the Saudis to Istanbul, according to a source familiar with the timing and route of the flights.

Flight-tracking data also backs up evidence of the planes' arrival in Istanbul.

The first flight from Riyadh arrived just after 3 a.m. local time Tuesday. The CCTV image from outside the consulate shows Khashoggi entering at 1:14 p.m.

A second flight from Riyadh landed in Istanbul at 5 p.m. It left an hour later, making a stopover in Cairo before returning to Riyadh. The first flight left Istanbul at 11:00 p.m.

On Wednesday, a Turkish newspaper, Sabah, published photos and names of the 15 men it said are the focus of the Turkish investigation.

Sabah said it "obtained photos of the mysterious intelligence team entering Turkey through Ataturk Airport." The photos alongside the names appear to have been taken from airport cameras. The Sabah report does not indicate the source of the material.

CNN has not been able to independently verify Sabah's account.

Police and intelligence officers searched one of the private planes before it departed Istanbul's Ataturk Airport. They also examined camera records from the day of Khashoggi's disappearance, according to Sabah.

Fiancée's agony

Khashoggi's fiancée told CNN that she fears for his fate. "He may have been kidnapped, abducted, or some harm may have come to him," she said in written answers to questions from CNN's Christiane Amanpour.

"Images in the media point to the possibility of an abduction or an assassination. I hope that it does not turn out to be murder as alleged by these images."

"Until official statements are made, it makes more sense to wait a bit longer and to see the final result as oppose to making a bold comment," she added, saying she did not feel comfortable enough to be interviewed on camera. "Until now no official document could be made available to prove that he did exit from there on his own," she said. "it has not been proven until now through official documents that he exited of his own accord."

Cengiz told CNN that she was questioned by Turkish investigators after Khashoggi's disappearance and has had a few calls with officials since. Saudi authorities have not contacted her, she said. Cengiz said she felt responsible for Khashoggi, and has been "in a state of deep confusion and sadness."

Yemeni Nobel Peace Prize laureate Yemeni Tawakkol Karman holds a picture of missing journalist Jamal Khashoggi during a demonstration in front of the Saudi Arabian consulate in Istanbul last Friday.

One activist familiar with the events leading up to Khashoggi's entering the consulate said Saudi officials had given the journalist assurances that it would be safe for him to enter. The Saudi consulate said "'No, don't worry about it, you're welcome here' ... So he didn't take the proper precaution," London-based activist Yahya Assiri told CNN.

"Some of his friends suggested that he go with a lawyer, or to let the Turkish police or intelligence know that he was going. He didn't notify anyone, just his fiancée and he went with her and they didn't let her in," he added.

"So he didn't take enough precaution. He had total trust in the state."