The Police Ombudsman said the probe into the IRA killing of Bertie Frazer was “a stark example of limited police record management”.
Bertie Frazer was shot dead in 1975 as he was leaving a farm where he often worked for a neighbour near Whitecross, Co Armagh.
Mr Frazer, a council worker and part-time member of the Ulster Defence Regiment (UDR), was 47 and married with nine children at the time of his murder.
His son was the prominent victims’ campaigner Willie Frazer.
Despite the absence of significant records, today’s report details concerns about aspects of the investigation, including the junior rank of the officer leading the murder probe, witness and suspect strategies, the disposal of a murder weapon and the lack of engagement with the Frazer family.
Speaking about today’s report Assistant Chief Constable Anthony McNally said: “Bertie Frazer was an innocent father of nine children murdered in a sickening, sectarian attack.
“The pain of such a devastating loss does not fade and my thoughts today are with the Frazer family who I met recently with the Chief Constable.
“We will take time to study the findings of this report which highlights the investigative failures, poor record management and a lack of engagement with Mr Frazer’s family by police.
“Policing has developed enormously over the past 50 years and the Police Service of Northern Ireland has greatly improved policies and procedures which guide how we approach criminal investigations today.
“Intelligence handling, training and investigative standards for detectives, forensic opportunities and family liaison processes today are unrecognisable from what were in place at the time of this terrible murder.”
Mr Frazer was killed while reversing his car, a Hillman Avenger, out of the farm’s driveway.
Two men approached the car and shot him.
The gunmen then pulled him from the driver’s seat and left him at the side of road before driving off in his car.
He was found a short time later and taken to Daisy Hill hospital where he was pronounced dead.
The ‘South Armagh Republican Action Force’, a South Armagh IRA unit, admitted responsibility for Mr Frazer’s murder, claiming it was in retaliation for the murders of two men, Sean Farmer and Colm McCartney.
Mr Farmer and Mr McCartney had been shot dead at an illegal vehicle checkpoint near Newtownhamilton, a week earlier.
No one has ever been prosecuted for Mr Frazer’s murder.