Chilling footage captured the moment a sniffer dog picked up the scent of blood in the apartment where Madeleine McCann was snatched from in May 2007.
The alarming development in the notorious cold case, which unfortunately did not lead anywhere, left investigators combing through the holiday rental in the Portuguese resort of Praia Da Luz with more questions than answers.
Video of the shock discovery reared its head again in 2019, after it featured in the Netflix documentary The Disappearance Of Madeleine McCann which was released that year.
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The eight-part series aimed to re-examine the infamous disappearance of Madeleine, the media coverage of the case and the investigation conducted by authorities, as well as how her parents Kate and Gerry dealt with her vanishing.
Months after the three-year-old first vanished on 3 May, 2007, puzzled Portuguese cops were struggling to find a lead and decided to bring in their canine counterparts for assistance.
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Expert dog handler Martin Grime, who has lent himself and his animals to help with crime scene investigations across the globe, travelled from the UK with his two spaniels, Eddie and Keela, to see if they could make any progress.
They headed to the resort where the McCann family had been staying in apartment 5A, to see if the dogs could pick up on anything which the human eye or forensics could not.
Explaining the abilities of his highly-trained pooches during an episode of The Disappearance Of Madeleine McCann, Martin said: "When the dog indicates in the field, it will either be human decomposition or human blood.
"The human decomposition is very persistent, very pungent to the point where we've been able to locate, in blind searches, graves 40 years after the body has been removed and the body was only there for a short period of time.
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"With blood, crime scene investigators have been to the house and somebody has cleaned the blood up to the point you can no longer see it. That doesn't mean there isn't any there to find.
"It might drip through the gap and run around the back of the floorboard, but odour will still be coming through the gap in the floorboards and the dog will pick it up and respond to it."
Although this means that is unlikely the animals will bypass any key evidence, it also suggests that they may have been detecting the scent of blood which may have been spilled long before the McCann's fateful family holiday.
Eddie - who was trained to smell traces of human corpses - was the first dog sent on a reconnaissance mission around the apartment.
US journalist Robbyn Swan said that the spaniel's 'behaviour changed the moment he came through the door'.
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"He became tense and aware," she explained. "The dog handler said Eddie didn't alert in any other situation except when he scented that which he was seeking: the scent of a human cadaver."
The footage from the Netflix doc shows Eddie wandering around the room, sniffing, before going over to a wardrobe and then turning to his handler and barking. He barks again when he sniffs behind a couch.
Keela - who was trained to only alert her handler only when she smelt human blood - then headed in alone for round two.
She also stopped in the same spot behind the couch.
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Both of the dogs were then brought outside to inspect the Renault Scenic hire car the McCanns had used during their trip.
The pair again both indicated to Martin that they had picked up on scents of human blood and a corpse in the boot and outside of the driver's door.
Madeleine's parents Kate and Gerry were named as persons of interest by Portuguese police shortly after the dogs were brought in, however, this was voided in 2008 when the case was archived.
When asked about the dogs findings that year, cardiologist Gerry said: "I can tell you that we've obviously looked at the evidence about cadaver dogs and they're incredibly unreliable."
Topics: Madeleine McCann, True Crime, Documentaries, Netflix, Dogs
Olivia Burke