Leaked CCTV footage has appeared to show a "body double" wearing Jamal Khashoggi's clothes just hours after he was killed.
The video, broadcast by CNN, shows the man strolling out of the Saudi consulate in Istanbul where the journalist was killed.
CNN cited a Turkish official describing the man as a "body double" and a member of group sent to Istanbul to target the 59-year-old writer.
CNN says the man walked out of the consulate via its back exit with an accomplice, then took a taxi to Istanbul's Sultan Ahmed Mosque, where he went into a bathroom and changed back out of the clothes and left.
- Video report by ITV News Correspondent Neil Connery
The death of Jamal Khashoggi, who wrote for the Guardian and Washington Post, was the subject of a statement to the Commons by Foreign Secretary Jeremy Hunt.
Mr Hunt condemned the killing and dismissed Saudi Arabia's official claims - first that Mr Khashoggi died in a fist fight and most recently that his "murder" was the result of a "rogue operation" - as "not credible".
But the Foreign Secretary told MPs, many of whom called for action against the Saudis, they must wait for the outcome of the investigation into Mr Khashoggi's death.
"Yes we do have vital security and commercial interests with Saudi Arabia and we do not wish just to blow them up, and it is quite wrong just to drop an inconvenient friend.
"But we in this country simply cannot tolerate such vile and brutal behaviour which can't be allowed to pass without consequence.
"Accountability must extend to the people that gave the orders for any crime, and not just to the people who were there on the ground," he said.
Saudi Arabia's King Salman and Crown Prince Mohammad bin Salman have reportedly called Mr Khashoggi's son.
The state-run Saudi Press Agency say the pair “expressed condolences” to Khashoggi's son Jamal on Monday after a weekend where pressure has mounted on the regime to provide answers about his death.
Khashoggi - a Washington Post contributor - had written columns critical of Prince Mohammad, the kingdom’s war in Yemen and its crackdown on activists and businessmen.
He was allegedly killed after seeking paperwork on 2 October for his forthcoming marriage.
- Conflicting reports of what happened
Initially, the Saudi regime said Khashoggi had left the consulate unharmed on 2 October.
Eighteen days later - on Friday - they admitted for the first time that he had been killed in a fight and that 18 Saudi nationals have been arrested.
On Saturday, US President Donald Trump announced he was “not satisfied” with their account and wanted to find out where the 59-year-old's body is.
On Sunday, Saudi Foreign Minister Adel al-Jubeir said that Khashoggi's killing was “a rogue operation” and that “we don't know where the body is.”
“The individuals who did this did this outside the scope of their authority,” he said.
“There obviously was a tremendous mistake made and what compounded the mistake was the attempt to try to cover up. That is unacceptable to the government.”
- How has the international community reacted to developments?
Turkish media reports that a 15-person Saudi team flew to Istanbul on October 2 knowing Khashoggi would arrive for a document he needed to get married.
Once he was inside the diplomatic mission, it is alleged the group questioned Khashoggi, cut off his fingers, killed and dismembered him.
Turkish President Recep Tayyip Erdogan has said that details of Khashoggi's killing "will be revealed in all its nakedness" in a speech in parliament on Tuesday.
On Monday, Theresa May condemned the killing, telling MPs: "I am sure the whole House will join me in condemning the killing of Jamal Khashoggi in the strongest possible terms... we must get to the truth of what happened."
In a joint statement, the foreign ministers of the UK, Germany and France called for an investigation into Mr Khashoggi's death on Sunday, saying this is “an urgent need for clarification of exactly what happened on October 2 - beyond the hypotheses that have been raised so far in the Saudi investigation, which need to be backed by facts to be considered credible.
“We will ultimately make our judgement based on the credibility of the further explanation we receive about what happened and our confidence that such a shameful event cannot and will not ever be repeated.
“We therefore ask for the investigation to be carried out thoroughly until responsibilities are clearly established and that there is proper accountability and due process for any crimes committed...
“Nothing can justify this killing and we condemn it in the strongest possible terms.”
Jeremy Hunt, Heiko Maas and Jean-Yves Le Drian continued: “Defending freedom of expression and a free press are key priorities for Germany, the United Kingdom and France.
“The threatening, attacking or killing of journalists, under any circumstances, is unacceptable and of utmost concern to our three nations.”