A U.S. government source said that United States intelligence agencies are increasingly convinced of the crown prince's culpability in the operation against Khashoggi, which they believe resulted in his death.
Khashoggi, a dissident living in self-imposed exile in the United States where he contributed to the Washington Post, vanished after entering the Saudi consulate in Istanbul on October 2. He left Turkey on Tuesday.
Kushner has been developing a relationship with the Crown Prince over the past several months and he has spoken to Salman several times over the past week.
"It certainly looks that way to me. It's very sad", Trump told reporters before boarding Air Force One on a political trip. "It's bad, bad stuff".
Asked what effect Saudi leaders would face if they are found to be responsible, he replied: "It will have to be very severe".
Khashoggi, who was often critical of the Saudi government in his reporting, disappeared after entering the Saudi Consulate in Istanbul on October 2. "Meanwhile hypocrites continue to trade weapons and prop up a Saudi regime wanted for murder, torture, starvation and genocide".
A Turkish forensic officer arrives at the Saudi consulate to conduct a new search over the disappearance and alleged slaying of Saudi writer Jamal Khashoggi, in Istanbul, early Thursday, Oct. 18, 2018.
Saudi Arabia opens up consulate after journalist vanishes
He said that "there was Saudi involvement" in whatever happened with the journalist, who wrote columns for The Washington Post . "This apparent enforced disappearance of Mr Khashoggi from the consulate of Saudi Arabia in Istanbul is of serious concern".
The four organizations said an global investigation should probe Saudi Arabia's role and aim to identify everyone responsible for ordering, planning and executing any operations related to Khashoggi's disappearance.
However, the investigation being led by the Saudis likely won't be impartial.
US Treasury Secretary Steven Mnuchin and UK International Trade Secretary Liam Fox have pulled out of an investment conference in Saudi Arabia.
Mnuchin had been under intense pressure to drop out of the conference that the White House had cast as intrinsic to its effort to dry up funds for terrorists.
Turkish media claim authorities have audio that shows he was tortured and murdered in the building after a 15-man "hit squad" entered the country.
Worldwide concern over the case has led to many business and political figures pulling out of an upcoming conference in the Saudi capital, Riyadh. But a number of European finance ministers and many top business executives have pulled out as worldwide pressure on Riyadh has intensified over Khashoggi.