Trump did not say Thursday what he based his conclusion on. But he says the consequences for the Saudis "will have to be very severe" if they are found to have killed him.
While much of what was discussed has yet to be announced, the US State Department said that Mr Pompeo had used the time to thank the king for his "commitment to a thorough, transparent investigation" into Mr Khashoggi's disappearance.
He went to the Saudi consulate in Istanbul to get documents he needed to marry his fiancée, Hatice Cengiz, a Turkish national who waited in vain outside for Khashoggi to return. The Saudis have denied involvement.
It took 13 days for Saudi authorities to allow Turkish Investigators access to the consulate for investigation.
Pompeo addressed reporters Thursday after briefing President Trump at the White House on his talks with leaders in Saudi Arabia and Turkey.
However, he refused to list what measures he would take, only saying that he would not choose to impose sanctions on the country for fear of losing its military sales orders with USA companies.
Khashoggi hadn't been seen since he entered the consulate to obtain marriage license papers on October 2, and evidence points to Khashoggi having been killed and dismembered.
Saudi Arabia on Sunday warned against any threats to exert economic sanctions or political pressure on the kingdom, saying it will respond with greater action given the kingdom's outsized role in the global economy.
"It sounded to me like maybe these could have been rogue killers", Trump said.
Trump said he has not sent the Federal Bureau of Investigation, stressing that he was not "American citizen". Saudi Arabia has called those allegations "baseless", but has been unable to explain what happened to him.
"We were going to be going to Saudi Arabia and meeting certain people that have been implicated in this, so you can imagine it just didn't feel like a trip we should be making", he said.
A Turkish official and a security source told Reuters on Monday that the authorities have an audio recording indicating that Khashoggi was killed in the consulate, without providing further details.
US media reported on Monday that Saudi Arabia would admit that the disappearance and alleged death of Khashoggi was the result of an interrogation gone wrong.
Pompeo also met with Saudi Crown Prince Mohammed bin Salman.
Khashoggi told MEE that one of the crown prince's closest aides was the person who first told the journalist he had fallen out of favour with the royal court. "We face our challenges together - the past, the day of, tomorrow", Prince Mohammed told Pompeo.
Earlier, a joint Saudi-Turkish team entered the Saudi Consulate in Istanbul to search it.
A cleaning crew walked into the consulate hours ahead of the investigative team's arrival.
Jamal Khashoggi haven foreknowledge of Mohammed Bin Salman [MBS] traits fled to United States and had since remained in USA and a "columnist" with Washington Post until he was preparing formalizing his paper for a marriage to his Turkish girlfriend, Hatice Cengiz, who apparently waited for Jamal Khashoggi outside the Saudi Arabia Consulate in Istanbul on the day Jamal Khashoggi "vanished" from the surface of the earth in what it is now been dubbed; "Investigation gone wrong" & "rogue elements" inside the Saudi Arabia Consulate in Istanbul, Turkey.
Saudi officials have called Turkish allegations that Saudi agents killed Khashoggi "baseless", but reports in US media on Tuesday suggested the Saudis may acknowledge the writer was killed at the consulate, perhaps as part of a botched interrogation.