Journalist Jamal Khashoggi's murder was "premeditated", Saudi Arabia's public prosecutor has been quoted as saying by Saudi state media.
The evidence for this 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.
The kingdom has since admitted he was murdered at the Saudi consulate in Istanbul, blaming a "rogue operation".
The official Saudi Press Agency 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.
Prince Mohammed vowed to punish those responsible on Wednesday, but media reports have quoted Turkish security sources as saying the operation was run by a top aide to the crown prince.
Saudi Arabia's latest announcement follows US media reports that CIA director Gina Haspel has heard audio recordings believed to capture the journalist's murder, reports BBC.
