Crash victims may have lain injured for three days
A dead man and a critically injured woman were found in a crashed car three days after the accident was reported to police, it has emerged.
Police Scotland found John Yuill and Lamara Bell in a blue Renault Clio just off the M9 near Stirling on Wednesday.
The force admitted the crash had been reported to them on Sunday morning but had not been followed up, despite the pair being reported missing by family.
The Police Investigations and Review Commissioner is to look into the case.
Ms Bell's family told BBC Scotland that they were angry and disgusted with the police's handling of the case.
They said she had suffered broken bones and had damaged kidneys because of dehydration, and had been placed in a medically induced coma.
There have been calls for a wider investigation into Police Scotland's response.
Mr Yuill, 28, and Ms Bell, 25, had been reported missing to police after last being seen in the company of friends in the Loch Earn area of Stirlingshire in a blue Clio in the early hours of Sunday.
It is understood the couple are from the Falkirk area. A friend of Mr Yuill's described him on Facebook as a "great guy and a brilliant dad".
Police Scotland had launched an appeal for information about the couple on Monday afternoon.
At the time, the force said their disappearance was "completely out of character".
It later released a photograph of the car they had been travelling in, but it has emerged that a report of a car off the road by the M9 on Sunday morning was not followed up by police.
The Police Investigations and Review Commissioner is to investigate, focusing on the call made to police on Sunday. A separate police investigation into the crash itself is ongoing.
Scottish Justice Secretary Michael Matheson, who is also a local MSP for Falkirk, said he wanted "early answers" about the tragedy, and said Police Scotland had assured him that all relevant information would be passed on to investigators.
Mid Scotland and Fife MSP Murdo Fraser said it was vital the "truly shocking incident" was investigated in depth.
He said: "People lying unattended at the side of the road for days is something you'd be surprised to encounter in the third world.
"The circumstances leading to this must be investigated as a matter of absolute urgency."
Scottish Liberal Democrat leader Willie Rennie said Mr Yuill and Ms Bell had been "failed" by police, and said the government should review whether a "wider independent investigation" is needed.
Assistant Chief Constable Kate Thomson of Police Scotland said officers had been called to the M9 southbound near junction 9 at about 09:50 on Wednesday following a report of a one-car crash involving a Renault Clio that had left the road.
Driver Mr Yuill was pronounced dead at the scene, while Ms Bell was taken to the Queen Elizabeth University Hospital in Glasgow, where she is in a critical condition.
She added: "We believe that this is connected to the ongoing missing persons search for John Yuill and Lamara Bell.
"As part of our investigation into this incident, it has come to light that a call was made to police late on Sunday morning regarding a car which was reported as being off the road.
"For reasons currently being investigated, that report was not followed up at the time. Following a call this morning, officers attended the scene.
"Officers have notified the families of this update. Our thoughts are with both families at this difficult time. A full investigation is currently under way to establish the full circumstances of the incident."