January 2010:

Gangland enforcer 'The Gerbil' is gunned down in an Asda car park in Glasgow. Superintendent Michael Orr is appointed senior investigating officer for Operation Trilby.

July 2010: Corrupt police officer Derek McLeod is interviewed as part of the investigation. He is later jailed.

Loading article content

Late 2010: The Crown Office asks for a review of Operation Trilby, including Detective Superintendent Michael Orr's interview with McLeod. Senior policeman Ruaraidh Nicolson conducts the investigation.

Early 2011: A criminal investigation is launched into Orr regarding Operation Trilby, conducted by Nicolson.

Late 2011: No proceedings are taken against Orr.

Late 2012: Orr makes a misconduct complaint about Nicolson.

December 2012: Nicolson is unveiled as an assistant chief constable at Police Scotland.

October 2013: Police watchdog PIRC finishes its investigation into Orr's complaint.

November 2013: Scottish Police Authority finds there was no misconduct by Nicolson, but it will write to the chief constable about "performance related" matters.