Journalist Jamal Khashoggi's murder was "premeditated", Saudi Arabia's public prosecutor been quoted as saying by Saudi state media.
The information came from a joint Saudi-Turkish task force, broadcaster al-Ekhbariya said.
It also reported that prosecutors were questioning suspects as a result of the joint investigation.
Saudi Arabia had initially denied all knowledge of the writer's whereabouts when he went missing on 2 October.
They have since admitted he was murdered at their consulate in Istanbul, blaming a "rogue operation".
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The official Saudi Press Agency also reported that Thursday saw Crown Prince Mohammed bin Salman chair the first meeting of a committee to reform the state's intelligence services, which was set up following Mr Khashoggi's death.
Saudi Arabia's latest announcement follows news that CIA director Gina Haspel has heard audio recordings believed to capture the journalist's murder.
Ms Haspel was allowed to listen to the audio during a visit to Turkey earlier this week.