Peter Murrell's arrest and police searches at his home and the SNP's headquarters have gone public in a dramatic fashion as part of Operation Branchform.
Police Scotland initiated the investigation 20 months ago and sought advice from the Crown Office and Procurator Fiscal Service (COPFS).
Peter Murrell was treated as a suspect and taken into custody for up to 12 hours of questioning.
He was released without charge pending further inquiries, but police can re-arrest him with conditions for up to 28 days.
Police will continue to investigate and gather evidence, seeking guidance from COPFS as needed.
If a suspect is charged, their legal status changes and more protections apply.
Prosecutors will consider the sufficiency of evidence and public interest before deciding whether to take the case to court.
COPFS can also instruct further inquiries or decide there is insufficient evidence for prosecution.
The law officers at the Crown Office, who are also principal legal advisors to the Scottish government, will not be involved in the decision about Mr Murrell's case.
Others will be responsible for determining the next steps in the Peter Murrell case.