Napolitano said. "We should be concerned about it because of Khashoggi's status, A, as a journalist, and B, as a lawful american resident, when the president says the king doesn't know anything about it, the king is probably telling the truth but the president is asking the wrong person".
The shares of Saudi Arabia in the Riyadh stock market plunged as much as 7 per cent on Sunday, much to the jitters of the investor.
Turkey said Erdogan "stressed forming a joint working group to probe the case".
"The kingdom affirms its total rejection of any threats and attempts to undermine it, whether by threatening to impose economic sanctions, using political pressures or repeating false accusations", the statement said.
Brent crude, the benchmark for more than half the world's oil, rose as much as 1.9 percent to $81.92 a barrel, before paring gains to trade at $81.24 by 6:58 a.m.in London.
The Saudi prosecutor has received instructions "to work quickly", so an announcement could happen within days, the Saudi official said.
The New York Times, citing an anonymous senior Turkish official, reported that the Saudi native was killed within a couple hours of entering the consulate by Saudi agents who dismembered his body, on order from the Saudi royal court.
The president has not said what measures his administration would take if Saudi Arabia is found to be responsible, but he made clear any punishment would not involve suspending Washington-Riyadh arms deals.
"The Saudi economy has vital and influential roles for the global economy", the source told SPA.
Following the disappearance of journalist and Washington Post contributor Jamal Khashoggi, a host of Western companies have distanced themselves from Saudi Arabia, leaving the Riyadh stock market in the doldrums.
The Saudi Gazette trumpeted: "Enough Is Enough", while the Arab News said: "Saudi Arabia "will not be bullied".
The Washington Post reported evidence has been shared with US authorities.
However, Saudi Arabia is facing substantial diplomatic pressure, and the fate of "Davos in the Desert", as well as the Saudi economy itself, appears to be in for a large degree of uncertainty.
Britain expects Riyadh to provide "a complete and detailed response" to questions over Khashoggi's disappearance, Prime Minister Theresa May's spokesman said on Monday.
The three-day event will be held next week and is also meant to showcase Prince Mohammed bin Salman's modernization plan for the desert kingdom.
But has has also expressed a reluctance to punish the kingdom economically or militarily, especially in terms of reducing the sale of billions of dollars worth of USA arms to the Saudis.
Those policies are all seen as initiatives of the crown prince, who has also presided over a roundup of activists and businessmen.