Portuguese cops initially believed Madeleine McCann's parents accidentally killed her with an overdose of Calpol

'The Disappearance of Madeleine McCann,' the eight-part documentary on Netflix which chronicles the 2007 disappearance of Madeleine McCann and the investigation since, has claimed that Portuguese detectives believed the girl's parents, Kate and Gerry, had killed Madeleine with an overdose of Calpol.

Madeleine disappeared on the evening of May 3, 2007, from her bed in a holiday apartment in Praia da Luz, a resort in the Algarve region of Portugal. She had been left there with her twin siblings by her parents, who had gone out for dinner, and there is still little clue to her whereabouts almost 12 years later.

It's been called 'the most heavily reported missing-person case in modern history' and as it is with cases of such magnitude, umpteen theories have been put forward as to how Madeleine vanished from the bedroom that fateful night, including one which suggests Kate and Gerry were responsible.

According to The Sun, the Portuguese police who were in charge of the investigations believed that Kate and Gerry, who were both briefly but officially named 'arguida,' suspects, had overdosed the young girl and then got rid of her body. Speaking the odd turn in the investigation, Anthony Summers, who co-wrote 'Looking for Madeleine' with Robbyn Swan in 2014, told the documentary producers, "By late summer there was an implication that they may have over-sedated her by administering a drug."

"Essentially the Portuguese cops' case against the McCann's involved the following: that she died by accident on May 3; that the supposed checks on the children had been concocted; that they had hidden their daughter's body... and that her body had subsequently been transported in the rental car they had rented some weeks later," Swan added.

But a few months later, forensic reports confirmed there was no evidence linking Madeleine's DNA to the holiday apartment or car, lifting the suspicion off Kate and Gerry. Jim Gamble, the head of the Child Exploitation and Online Protection Command (CEOP) at the time, said the DNA made it obvious the Portuguese police's lead was a "red herring," but that it was a dangerous red herring because of their belief that they had a smoking gun.

However, it was still a theory heavily advocated by Inspector Gonçalo Amaral, the head of the criminal police who was initially appointed as the coordinator of the inquiry into Madeleine's disappearance. After his removal as coordinator in October 2007 over his comments to a newspaper claiming British police were only pursuing leads helpful to the McCanns, he went to publish a book called Maddie: A Verdade da Mentira ("Maddie: The Truth of the Lie") where he claimed Madeleine had died in an accident in the apartment and that, to cover it up, the McCanns had faked an abduction.

Sandra Felgueiras, a Portuguese journalist who covered the disappearance, revealed she felt "lied to" by her police sources, who kept trying to tell her that the evidence against Kate and Gerry was damning. "When this happened I understood that the intention of those cops that were inside this investigation was not honest," she said in the documentary.

Meanwhile, Maddie's parents have objected to the Netflix documentary on their daughter's disappearance, saying it "won’t help" the search. The family believes the controversial new film could "fuel conspiracy theorists", their spokesman said.

Watch the trailer for 'The Disappearance of Madeleine McCann' here: