Police investigations of the deaths of Kevin McLeod and Kevin Gillies have led to criticism from the families of the victims.
The body of Mr McLeod was found in Wick Harbour in February 1997, with massive internal injuries.
During the original investigation, police put Mr McLeod's injuries down to falling on a 3ft bollard before plunging into the harbour.
His parents, Hugh and June, rejected this and have always maintained that the injuries were not accidental.
They also expressed concern that no door-to-door enquiries were undertaken during the original police inquiry and have campaigned for the case to be reopened.
The McLeod family carried out their own investigation which established that there was an assault on Kevin on the evening that he died.
Fisherman Kevin Gillies, 22, was killed in a Skye traffic accident on Christmas Eve in 1999.
Independent inquiry
The vehicle which hit him was allowed to leave the scene before the investigation had been completed.
Experts for the BBC's Frontline Scotland programme said that basic police procedures had not been followed.
Tory MSP for the Highlands and Islands, Mary Scanlon, has called for an independent inquiry into what happened to restore confidence in the force.
She said: "The Gillies' and McLeods, like all people in the Highlands, had total faith and trust in the Northern Constabulary.
"Week by week, month by month, year by year, that faith and trust has been eroded.
"It is now for Northern Constabulary to come forward with the answers to bring back trust and confidence in the police force in the Highlands."
Chief constable Ian Latimer said that lessons have already been learned.
He said: "Errors were made. Our own internal review acknowledged that errors had been made by individual officers in the initial scene management.
"The important point is we have learned from our mistakes.
The findings of the investigations have not been challenged by fatal accident inquiry or by the procurator fiscal service, he said.
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