A damning report upheld a dozen complaints by the family of Colin Marr, who died from a single stab wound to the chest in 2007 after an argument with his fiancée Candice Bonar at a house they shared in Lochgelly, Fife.
In one of the most critical verdicts ever handed down by the Police Investigations & Review Commissioner, officers were lambasted for destroying DNA evidence against protocol, failing to carry out an internal investigation into the force's shortcomings after Marr's death, and not meeting with Marr's family to take statements until after his body was cremated.
Scottish Liberal Democrats leader Willie Rennie MSP for Mid Scotland and Fife, said "unprofessional conduct" by police "prev-ented the truth emerging".
Bonar told detectives at the scene that the 23-year-old stabbed himself because she had ended their seven-year relationship over an alleged infidelity, which he denied.
Officers accepted her version of events and the case was closed. A subsequent nine-day Fatal Accident Inquiry was unable to determine who inflicted the fatal wound, leaving Marr's loved ones in limbo. Bonar later emigrated to Australia where she now lives with her new partner, Bradley, and their young daughter.
But Colin Marr's mother and stepfather, Margaret and Stuart Graham, have always refused to accept Bonar's story and their campaign for justice led to the Crown Office ordering a review led by retired Strathclyde Police Detective Superintendent David Swindle in 2011. He ruled that Marr's death was "suspicious" and said it "should have been treated as such at the beginning".
A year-long review of the way Fife Constabulary handled the death of Colin Marr and complaints against the force by his family is to be published today.
Candice Bonar was contacted for comment but did not respond.