Well I think (in fact I know from personal experience) that after an incident like this people do get very confused. They start imagining they have seen all sorts of suspicious things in the previous hours and days.
Doubtless police will have had many witnesses like this saying they saw people - people not doing anything suspicious: just being there around where the incident later took place. It's common to incidents everywhere.
What's common to all the statements used in Madeleine was here is that the people seen (or later said to have been seen) weren't doing anything suspicious: they're just described as looking 'odd'. People are desperate to help after incidents and can create something from nothing - very easily.
Are you real, Lyall? Tasmin saw a man who she had seen also on at least one other occasion staring at 5A, again standing right by 5A garden wall staring into the apartment Are you saying that that is not suspicious ?
Of course most people in PdL will Not have seen anything suspicious, and all will have appeared quiet and normal to them. Criminals do not go around with big black arrows all over them and a bag marked SWAG !
But here there are sufficient observations to have a definite pattern of suspicious behaviour beforehand.