Benice what do you think SY are basing that belief on ? Could it be the cadaver dog alerts perhaps ?
As I said before - I believe they are basing it on the information from the UK parents - particularly on the MO of the person who assaulted their children. Especially if there was a common denominator.
I don't know what SY think about the dogs alerts. Except to say the alerts haven't prevented them from ruling out the McCanns and their friends from the enquiry.
One can only speculate, but IMO it is likely that with there being so many different reasons why Eddie would alert - which do not involve a cadaver being in 5A - coupled with other reasons, - such as timelines which don't fit in with the time required for cadaver contamination to be present etc. etc. they may have dismissed the possibility that Eddies alerts could have related to Madeleine.
IMO if Madeleine did die in 5A - I think SY would believe she was removed very quickly - mainly to remove DNA evidence from the scene.