TBA

The footage of sniffer dogs searching the McCann's holiday apartment and rental car was one of the most jarring moments to emerge from the investigation into the disappearance of Madeleine.

Gerry and Kate McCann, who resolutely claim Maddie was abducted, have always questioned the reliability and objectivity of British dogs Eddie and Keela, despite their impressive credentials.

During those searches, Eddie, a cadaver dog trained to detect the odour of a dead body, is seen alerting and barking in Kate and Gerry's bedroom of holiday apartment 5A.

Eddie also "hits" and barks loudly behind a blue couch in the living room of the Praia da Luz apartment where the McCann family stayed in 2007.

A second sniffer dog, Keela, trained only to detect human blood, also alerted behind the couch.

Six days later, on August 6, both dogs alerted on a Renault Scenic rental car the McCann's hired 25 days after Madeleine vanished.

Though the work of cadaver and blood dogs cannot be submitted as evidence, investigators hoped Eddie and Keela would provide crucial clues as to what might have happened to Maddie on May 3.

Just days after the dogs finished searching, the McCanns were sensationally named 'arguidos' (a person being questioned under caution) by Portugal's Policia Judiciaria. The 'arguido' status was lifted from Kate and Gerry after 10 months.

US criminal profiler Pat Brown, who for almost a decade has studied the case and written extensively on Madeleine's disappearance, described Kate and Gerry's reaction to the sniffer dogs as "just not right".

"What dogs do is either help you find a body or they help you understand what happened to a body or that there has been a body there," Brown told Nine.com.au.

"[The McCann's] reaction to the dogs hitting on things, their reaction and behaviour was incorrect. It didn't make sense," Brown claimed.

Brown believed it strange that the McCann's did not appear "very concerned" that the work of the dogs indicated a dead body had been in their Algarve holiday apartment.

 The crime expert, who as part of her repertoire analyses human behaviour, pointed out that the McCanns could just be "off the charts as an anomaly" when it comes to ways people might typically react to events. Brown added it was in no way a singular sign of anything untoward.

Another possible explanation, unrelated to Brown's analysis, was that Kate and Gerry simply could not bring themselves to concede Maddie had died.

During a 2009 television interview with Portuguese journalist Sandra Felgueira, Gerry McCann was asked about the cadaver dogs alerting to the scent of a dead body in apartment 5A and their rental car.

"I can tell you that we've obviously looked at evidence about cadaver dogs and they're incredibly unreliable," McCann replied.

Kate McCann made similar assertions in the book she wrote about her family's ordeal, titled Madeleine.

Sniffer dogs Eddie and Keela had been brought to Praia da Luz in July 2007 at the request of Mark Harrison, a British investigator and national adviser to UK police, who specialises in searching for people missing, abducted or murdered.

 Harrison's remit from Portugal's Policia Judiciaria was to solely explore the possibility that Madeleine had been murdered and her body was concealed in surrounding areas, according to police files.

In one of his preliminary reports, Harrison said any alerts by the dogs may suggest that a body had been in the property and then removed. He added "no inference can be drawn as to whether a human cadaver has previously been in any location without other supporting physical evidence".

As Harrison delivered his report, Policia Judiciaria were submitting and awaiting results on forensic evidence taken from behind the sofa in apartment 5A and the boot of the Renault car.

A British scientist from the now defunct Forensic Science Service, John Lowe, came back to Portugal's detectives with forensic results that appeared inconclusive but open to interpretation.

In a September 3, 2007 email, Lowe stated the swab taken from behind the sofa produced an "incomplete DNA result".

However, Lowe continued: "All of the confirmed DNA components within this result match the corresponding components in the DNA profile of Madeline McCann".

Lowe said his testing of the swab from behind the sofa could not determine what kind of bodily fluid made up the DNA sample.

But, as would be later noted by the handler of sniffer dog Keela, his canine was only trained to alert to human blood, nothing else.

The forensics taken from the boot of the Renault Scenic was judged by Lowe to be "too complex for meaningful inclusion and interpretation".

However, Lowe also concluded that 15 of 19 components present in the sample could be linked to Madeleine.

Though "complex", the forensic results from the rental car mean it was possible that Madeleine may have been present in the Renault Scenic.

In his book, Goncalo Amaral, the Portuguese detective the McCanns tried to silence, said his team confirmed nobody had ever died in apartment 5A, prior to the arrival of Madeleine's family.

Martin Grime, the handler of cadaver dog Eddie, said the dog appeared immediately "very excited" when they arrived at the door of 5A.

"As soon as [Eddie] has come into the house he's picked up a scent that he recognises," Grimes said in a police interview in August 2007.

He detailed how the dog barked in two places in the apartment, in the bedroom close to a large wardrobe with shelves, and behind the sofa.

"What we should understand with this dog is that he only barks when he finds something, he won't bark at any other times. He won't bark at other dogs, he won't bark at strangers, he won't bark when somebody knocks on the door or anything like that," Grimes said in the interview.

Grimes also added in the police report that the work of his dogs Eddie and Keela should be backed up and confirmed with corroborating evidence, such as forensics.

Cadaver dogs are used widely by Australian police forces to locate dead and missing bodies, according to NSW Dog Unit Commander, Acting Superintendent Sheridan Waldau.

A/Supt Waldau told Nine.com.au he was unsure how cadaver dogs were used in the McCann case, but that his unit can "detect minute amounts of blood or remains across large designated areas".

"Cadaver dogs … have proven vital to uncovering evidence in past investigations," he added.

Several studies have tried to pinpoint the minimum length of time it takes for a dead body to emit a cadaver odour.

A 2007 study from the University of Bern in Switzerland recorded highly trained dogs accurately alerting to cadaver scent within three hours of a person dying.

Other research has shown human corpses will begin to emit cadaver dogs can detect 90 minutes after death.

CORRECTION: On March 21 this article was changed to reflect that 'arguido' status was lifted (instead of 'cleared') from Kate and Gerry McCann.