When Colin Marr, 23, from Inverkeithing, Fife, died in July 2007 from a stab wound, following an argument with his girlfriend, Fife Police ruled his death was suicide.
But Mr Marr’s family, including his mother Margaret Graham and Stuart Graham, his stepfather, have always challenged that verdict. They fought for a fatal accident inquiry, which was held in 2011.
At the end of the three-week inquiry, Sheriff Alastair Dunlop said he could not determine whether the death was suicide or homicide.
An independent review, which was conducted following a request by the Crown Office and published in July 2012, found serious failings in the initial investigation by Fife Constabulary.
Throughout their campaign, the family has been supported by MSP Willie Rennie who has written to Fife police, backing calls for further investigation.
In a joint statement, Mr and Mrs Graham, said: “We have spent over five years following due process in a desperate attempt to have our complaints about the police mishandling of our son’s tragic and sudden death heard.
“The actions taken by Police Scotland, in dealing with the glaringly obvious attempt by Fife police to whitewash the actions of their officer(s), have caused further delays in dealing with our substantiated issues, and will most likely allow another officer to retire before facing accountability.
“We are quite literally at the end of our tether. This fight is not based upon emotion but down to the simple and fundamental fact that we have been failed in the worst way possible.
“What we are asking is not unachievable or unattainable. We want to see immediate action against the senior investigating officer who led from October 2008 and we want to see a full investigation, independent of police, into the actions of Fife police on the night of our son’s death and in the aftermath, to make accountable those who failed in their duty.”
Mr Marr’s girlfriend, Candice Bonar, told police he stabbed himself in the chest with a kitchen knife at their home in Lochgelly on 10 July 2007, after she accused him of cheating on her. She has since moved to Australia.
Mr Rennie said: “The Grahams have been subjected to considerable pain in the years following the death of their son Colin. For such fundamental errors to have been made at the beginning of the investigation is in itself a tragedy but the subsequent failings have compounded that initial failure.”
Police Scotland said it had asked the Police Investigations and Review Commissioner (PIRC) to carry out an independent inquiry. A PIRC spokesman said: “In August, the commissioner received a request to carry out an independent review. We have received a significant amount of paperwork and the review is under way.”