Sometimes there are pointers that something may be amiss that when looked at in retrospect immediately fall into place.
There certainly seems to have been something unique about apartment 5a when witness accounts are looked at; I doubt it was usual for all apartments to be scrutinised in the way that particular apartment was over what appeared to be an extended period.
I don't think it could have been staked out for the purpose of burglary; there are no reports of a burglary taking place there despite the targeting of other apartments in the block.
A Mark Warner nanny was shocked to encounter a man lurking in the darkness at the front of the apartment block; this frightening incident was reported to her employers who apparently did not think it important enough to inform the police about it.
They also took good care not to inform guests about intrusions at the resort.
“ … six months before the incident with Maddie there could have been an abduction attempt from the same apartment that was let to the McCann family”.
“ … she was working as a babysitter in the same apartment that the girl was abducted from. She confirms that the events occurred on a Thursday night. Thursday nights were known as the "tennis nights" and on that night the girl's parents were out playing tennis.”
“She left by the front door and in the darkness, by the movement sensitive lights, she saw something move and thought its was a rat. To her surprise, when she examined it closely, she saw that it was a brown shoe of a man who was watching the dark zone outside the apartments. She shouted and the man came out of the darkness, the lights were activated at which point he came towards her and said "No, no".
She said the man was aged between 25 - 35 years, with a Mediterranean aspect with tight black curly hair. She is certain that he had a Mediterranean accent, surely Portuguese. From the only two words he said. He wore light coloured trousers and a blue checked shirt.
After this she returned to the apartment in a state of shock,
it was obvious that there was no good reason for him to be hiding in the darkness outside the apartment.”
http://www.mccannpjfiles.co.uk/PJ/MARGARET_HALL.htm