"It is tragic that it took his death to get the Saudi authorities to grant them the freedom to travel", Slim told AFP.
US President Donald Trump has stated that it will be up to the US Congress to decide what to do in response to the killing.
Turkish officials and some US lawmakers allege the crown prince ordered the operation in which Jamal Khashoggi killed.
After first insisting Khashoggi left the consulate unharmed, Saudi authorities said he was killed in an argument that degenerated into a brawl, then admitted he was murdered before finally accepting what Turkey had said earlier - that he was killed in a premeditated hit.
Mevlut Cavusoglu is Turkey's foreign minister.
Turkey said it believed a hit squad of Saudi nationals had travelled to Istanbul with the sole objective of killing Khashoggi, a former member of the Saudi elite who became critical of the current government's administration in his country.
Saudi Arabia has detained 18 people and dismissed five senior government officials as part of the investigation into Khashoggi's murder.
According to the statement, a joint Saudi-Turkish investigative team "indicates that the suspects in the incident had committed their act with a premeditated intention".
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But to match its sparkling combination of pearls and diamonds, was a rather impressive necklace never seen on the Duchess before. The tiara is over one hundred years old and now belongs to the Queen , though it once belonged to Queen Mary .
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The killing of journalist and US resident Jamal Khashoggi by Saudi agents has stirred calls for USA sanctions on the kingdom. The pledge comes despite Saudi Arabia's previous threats to retaliate to any sanctions with "greater action".
Saudi King Salman and Prince Mohammed met Salah and Khashoggi's brother Sahel at the royal palace in Riyadh on Tuesday.
Saudi journalist Jamal Khashoggi was the victim of an "extrajudicial execution" committed by the Saudi state, a United Nations expert said Thursday, calling for an worldwide investigation.
A photograph of the meeting published by the official Saudi Press Agency showed Salah staring coldly at the prince as the pair shook hands.
Dozens of people stood vigil outside the Saudi consulate in Istanbul on Thursday to demand justice. One, his hands painted red, wore a mask depicting the face of Prince Mohammed.
It also came two days after Turkish President Recep Tayyip Erdogan gave a speech calling Khashoggi's killing "brutal" and "planned" while demanding that the perpetrators be extradited to Turkey.
King Salman also spoke to Vladimir Putin on Thursday, telling the Russian president that the Saudi government was determined to hold the guilty parties accountable and to make sure "they receive their punishment".
Saudi Arabia is the lynchpin of a USA -backed regional bloc against Iran but the crisis has strained Riyadh's relations with the West. Dozens of Western officials, bankers and executives shunned a big investment conference in Riyadh this week.
"But we have enough right now to determine that the government of Saudi Arabia is responsible and is implicated".