Police are duty bound to look at all the evidence and that included the dog alerts which were certainly suggestive of something untoward. Add to this the fact that the FSS were telling the Portuguese one thing but failing to back it up in their final report apparently.
The part which sells it for me is that the cadaver dogs only showed an interest in McCann related objects and accomodation. I for one don't believe in serial coincidences.
IMO if Keela had been sent into the other apartments, she would have alerted to blood.
This is because
a) I DO believe Grime's claim that she could sniff out miniscule amounts of blood deposited decades ago - and that the detection of blood was her
only expertise - so -unlike Eddie - there was never any question over what it was she was alerting to.
and
b)
I do NOT believe it is possible that not a single drop of blood had ever been in situ in any part of even ONE other apartment, let alone THREE of them, in the very long time scale that Keela could be relied on to make a detection.
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It all depended on .... 'time allowed to search' .....IMO. For instance Keela did not alert to the white curtain in 5A on her first visit - it took a second visit and a second search before she did that.
The co-incidence IMO is that it just happened to be all the apartments where Keela was NOT deployed that no alerts to blood were made.
AIMHO