A woman was found in a critical condition next to a dead man in a car – three days after the crash.
Police in Scotland have been searching for 28-year-old John Yuill and 25-year-old Lamara Bell since they were reported missing.
The couple were last seen in the company of friends on the south shore of Loch Earn, Stirlingshire, in the early hours of Sunday.
A call was made to police late on Sunday morning about a car which was reported as being off the road on the M9.
However, it has emerged that this was not followed up.
A separate report was made just before 10am on Wednesday.
The matter has been referred to the PIRC by the Crown Office.