THE family of a man who died from a stab wound to the chest following a row with his girlfriend say they have made a breakthrough in their fight to uncover the facts behind his death.

Colin Marr passed away from his injuries almost seven years ago in Lochgelly, Fife, following an altercation with his girlfriend.

His death was ruled as suicide at the time, but an independent review later established that a catalogue of errors were made by Fife Police on the night.

The case has since been re-opened by Police Scotland. At the family's behest, retired officer Tony Whittle, former head of CID at West Yorkshire Police, has compiled two new reports on the events surrounding Mr Marr's death and has submitted them to the Crown Office in a bid to bring about a criminal investigation.

Mr Marr's mother and step father, Margaret and Stuart Graham, have been working with Mr Whittle to investigate aspects of the case.

Mr Graham said: "The professional guidance and expert help from Tony Whittle has proved to be the turning point in our quest for the truth.

"These last few months have given us hope that we may finally uncover the exact circumstances in which our much loved, and desperately missed son died."

Mr Marr, 23, died in July 2007 from a single stab wound following a domestic row with his fiancee Candice Bonar. Fife Police, who carried out the initial investigation, were criticised for their handling of the case and the former police force has formally apologised for their immediate response to the death.

Mr Whittle spent many years as a Senior Investigating Officer, specialising in cases of homicide and is still involved in teaching homicide investigation techniques.

He said: "I first heard about the case in November 2012 and it soon became obvious to me that Colin's family had been very badly let down by the system.

"When I was later contacted by Stuart Graham he told me that the family's only wish was to discover the truth; and I agreed to help them.

"Having looked closely at the evidence, I believe we have identified a number of key issues and that a thorough investigation of these issues will help to uncover the truth."

In light of the new information, the family is now appealing to anyone with any knowledge from the night in question or who may have been a witness to come forward and speak in confidence to an independent solicitors' firm.

Scottish Liberal Democrat Leader, and Mid Scotland and Fife MSP, Willie Rennie has been supporting the family in their quest for the truth.

He said: "I would urge members of the public particularly my constituents to cast their memories back and dig deep for any shred of information which may prove useful in the investigation.

"It has been a long, hard road for this family and I truly hope this latest appeal will help to bring some closure."

A spokesman for the Crown Office confirmed the receipt of correspondence from Mr Marr's family. "It is currently under consideration by the procurator fiscal," he said.