POLICE have vowed not to give up in the search for answers over the disappearance and suspected murder of York chef Claudia Lawrence.

This year saw the biggest developments in the six years since her disappearance, as Operation Essence, a review into the initial investigation, led to the arrests of four men on suspicion of murder, but her family and friends faced another Christmas without knowing what happened or where she is.

The men, who are all from the York area and aged in their fifties, were arrested in March and April but later released from police bail. However, the force said a file of evidence has been presented to the Crown Prosecution Service by North Yorkshire Police's Major Crimes Unit.

In coming months, the CPS are expected to consider the evidence before them and advise North Yorkshire Police on how the investigation should proceed, and whether any charges or prosecutions should be brought.

Claudia was 35 when she disappeared in 2009. She never arrived for her morning shift at the University of York on March 19, 2009, but had been seen on CCTV and had spoken to her parents the previous evening.

The initial investigation into Claudia's disappearance later became a murder inquiry with more than 100 officers working on the case at one point. The charity Crimestoppers later offered a £10,000 reward for information which could assist the investigation, and North Yorkshire Police spent more than £750,000 spent on the investigation by 2010.

So far, Operation Essence has cost North Yorkshire Police around £400,000, with work continuing within the MCU to review a considerable amount of evidence from 2009 and more recently.

The Press, The Gazette and Herald, all media outlets and members of the public have been asked to avoid identifying the arrested parties, even after they have been released from police bail.