A "blood-curdling scream" was heard on the night a mother and son disappeared more than 45 years ago, the High Court in Inverness has been told.
William MacDowell, 80, has been accused of murdering Renee MacRae and their three-year-old son Andrew MacRae.
He denies the charges and his lawyers have lodged special defences of incrimination and alibi.
Catherine Johnstone said her late mother, Eva McQueen, told of hearing the scream.
Mr MacDowell, of Penrith, Cumbria, has been accused of murdering Mrs MacRae and their son at a lay-by on the A9 at Dalmagarry, south of Inverness, or elsewhere on 12 November 1976.
He has also been accused of disposing of their bodies and setting fire to a car.
Giving evidence on the first day of the trial, Mrs Johnstone told the court she had been living with her parents at a farmhouse near the lay-by at Dalmagarry at the time.
Mrs Johnstone was asked by advocate depute Alex Prentice KC: "Did your mother ever make any reference to something that night?"
She replied: "She said she heard a blood-curdling scream that night. She couldn't detect where it came from. She said it was about 7.30pm to 8pm."
Mrs Johnstone also told the court how she had seen a car with no lights sitting in a lay-by and remembered a 4×4-type vehicle travelling south at speed as she drove into Inverness that night between the same times.
Det Ch Insp Brian Geddes read a statement taken by officers from Mrs Johnstone's mother, who died in 2014, which said she and her husband Charles McQueen were leaving their farmhouse when she heard a "distinct screech".
The jury also heard a number of accounts about a car which was seen on fire in the lay-by at Dalmagarry.
Richard Grant, 65, who was an assistant train driver at the time, recalled seeing a car ablaze and that it was reported to the local signalman.
The court also heard an account read by a senior police officer of a bus driver, now deceased, who saw the car on fire and pulled into the lay-by to investigate.
The bus driver confirmed the registration of the car was that of a blue BMW, normally driven by Mrs Macrae, although no sign was found of the occupants.
Mr MacDowell has been accused of murdering Mrs MacRae and their son Andrew by unknown means.
He also faces a charge alleging he disposed of their bodies, personal effects and a pushchair and of setting fire to a BMW car, and disposing of a Volvo car's boot hatch.
Prosecutors claim this was done to conceal his crimes and to avoid detection, arrest and prosecution and in an attempt to defeat the ends of justice.
Mr MacDowell, who appeared in court in a wheelchair, denies all the charges and his lawyers have lodged special defences of incrimination and alibi.
The jury was told Mr MacDowell was not at the scene of the alleged murders and that he spent the night at home.
The court heard he had been at his work, Hugh Macrae Builders Limited, and when he left that evening he went to the Mercury Motor Inn, where he was with James MacBeath, Hamilton Young and John Davenport.
Then, the jury heard, he travelled back to work before visiting a store. Afterwards, he is said to have driven home via the A9, getting back to his house at about 20:15.
The defence claims Mrs MacRae's husband Gordon MacRae, whom she was separated from, committed the offences together with persons unknown.
The court was told Mr MacRae married Mrs MacRae on 17 May 1963, but they split in 1975.
The jury heard that in the July of the following year, she moved into Cradlehall Park, near Inverness, in a home provided by her estranged husband.
The trial before Lord Armstrong continues.
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