Police Commissioner Karl O'Callaghan has conceded that "all identified lines of enquiries have been exhausted" in the cold-case investigation into the death of Corryn Rayney.

It is a year ago Friday since Mr O'Callaghan announced expert investigators from Queensland, New South Wales and the UK would embark on a cold case review of the murder investigation in tandem with fresh investigators from WA Police.

But he apologised to Ms Rayney's family on Thursday as he announced Operation Delve had found "insufficient evidence to charge any person with an offence" in relation to her death.

"This was about starting over," the commissioner said at a media conference.



"Unfortunately the passage of time has taken its toll.