The process for Fatal Accident Inquiries (FAIs) must be fixed in Scotland, according to Willie Rennie.
Four years after the deaths of John Yuill and Lamara Bell following a crash on the M9, the Scottish Lib Dem leader said there must now be a full review into the inquiry system.
Mr Yuill and Ms Bell lay undiscovered in their car for three days after it crashed off the motorway, despite the incident being reported to Police Scotland at the time.
A FAI into the 2015 incident, however, has still not been held.
Mr Rennie said: “The agony for the families and friends of Lamara and John goes on and on. The initial event was tragic, the delays are unforgivable.
“The current FAI process urgently needs to be fixed. This should be a people-centred system, but at the moment it’s bureaucratic and slow.
“Families are facing agonising waits for closure.
“If these inquiries can’t lead to timely lessons learned, then what is their value?”
Mr Rennie said that his party wants the Scottish Government to commission a full independent review of the FAI system.
He has indicated that the review should be used to investigate and propose reforms addressing protracted timescales, structural barriers and lack of public confidence in the process, including whether the FAI system should be removed from the Crown Office and Procurator Fiscal Service.
A Scottish Government spokesman said: “Our deepest sympathies remain with the families of Lamara Bell and John Yuill.
“Responsibility for the investigation of death in Scotland lies with the Lord Advocate, who acts independently of ministers.”