What I don't understand is why the McCanns' private detectives became involved with Marcos Correia at all
I mean, they were employed by the McCanns to follow the thesis that Madeleine was alive and findable ... were they not ?
So why did they pay the expenses of this man who purported that Madeleine had died in horrific circumstances based on nothing more than an grotesquely graphic vision/dream he had ?
Why did they pay attention to him at all ?
Two things here. Firstly, it was Método 3 who paid Correia. We also know that they in turn were being funded by Kennedy and/or the Madeleine Fund but we don't know at what stage, if at all, the McCanns personally authorized any payments to Correia. We do know the McCanns weren't at all happy with his involvement so take out of that what you may.
Remember too that Correua admitted that Madeleine’s parents preferred to spend the decreasing money from the Madeleine Fund in mainly following leads that placed the hypothesis that their daughter was still alive, they dismissed the possibility of paying professional divers to scrutinize the dam. That Correia offered to pay for the first phase of the searches in the dam and later received much support (even financial) from mediums and spiritists who believed in and corroborated his theory.
Secondly, one has to remember that Correia initially claimed that underworld sources had told him that Madeleine's body could be found at the Arade Dam. He later changed this and claimed that the information came to him in a vision.
I don't have time at the moment but it would be extremely useful to have a timeline of events and who did what and when.