Forensic experts have shared how they used blood and soil analysis to help convict the killer of a Highland mother and son decades after their disappearance.
Renee MacRae’s car was discovered engulfed in flames at the side of the A9 in Dalmagarry on the evening of November 12, 1976.
She and her three-year-old son, Andrew, were nowhere to be seen – and have not been found since.
As their investigation progressed, police started to suspect her married lover Bill McDowell may be responsible for their deaths, but a lack of evidence meant the case went cold.
Now, the re-examination of evidence by experts in the 2000s has been explored in a new BBC documentary.
The work of soil specialist Lorna Dawson and blood analyst Chris Gannicliffe helped lead to the conviction of MacDowell in 2022 – 46 years after the pair’s disappearance.
Experts from Renee and Andrew MacRae case topic of BBC show
Mr Gannicliffe was the final witness during the trial and explained to the court how a “blood deposit” may have ended up in the boot of the car.
Police found the blood stain on the underside of the carpet in 1976 but were only able to determine the blood type at that time.
When he joined the investigation in the 2000s, the blood spatter analyst could use luminol to uncover more blood on the opposite side of the carpet.
He told Expert Witness: “This might suggest that something has taken place to, in some way, clean it or wipe it away.”
By using horse blood to show what quantity would have been needed to create a “soaked-through” stain of that size, Mr Gannicliffe helped establish the suggestion of criminal violence at the scene.
The expert was also able test the sample against DNA from Mrs MacRae’s hairbrush to confirm it was her blood.
Analysing samples decades later
Soil specialist Lorna Dawson, who works from the James Hutton Institute in Aberdeen, was able to prove Mr MacDowell had lied about his whereabouts on the night the mother and son disappeared.
She told the documentary: “The suspect had said that his vehicle had only been in and around the Inverness area, and certainly he hadn’t said that he hadn’t driven south of a place called Daviot.
“Two or three miles south of there was Dalmagarry lay-by, where Mrs MacRae and her son’s vehicle was burnt out.”
Soil samples were collected from MacDowell’s car in 1976 but they were never analysed.
Professor Dawson was able to extract and prepare each sample for “a whole suite” of analyses and found his car must have travelled south of Daviot on that night.
She said: “The vehicle samples were of a granitic paint material, and of the reference samples, the ones that were closest in that characteristics were two that were down south of Daviot at and around Dalmagarry lay-by.”
Expert Witness: Blood on the Carpet is available to watch on BBC iPlayer.
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