I don't think it was very much at all to do with Lori Campbell who mainly gets the "credit" for whistle blowing or anyone else.
The PJ very much had their suspicions about him the least of it being what might be called eccentric behaviour and based on the information in the files they would have been seriously remiss in their duty had they not checked out the information they had on him.
In this instance the arguido status was instituted in appropriate and proper circumstances which protected his rights.
Given what has come out since regarding official thinking it was probably the time to do the same for the Drs McCann when it might have afforded them some protection and rights ... rather than being used as a salvo in a personal war.
Read the files and it will become apparent why the PJ acted correctly, that was their job, the fact that they found no further evidence to back up initial suspicions ... which were not as a result of 'odd' behaviour ... is part of the process.
There is a (genuinely excellent) profile of Robert Murat in
The Times that casts Murat's mode of behaviour in an entirely light.
It seems that, from way before events of PdL 2007, he was the sort of neighbour that would be a God-send to have, always eager to help, always on-hand, nothing, ever, too much trouble, to an extent that occasionally you might think he was
too enthusiastic and eager.
I think, when you read that profile, it casts his way of conducting himself in the wake of Madeleine's disappearance in a very different light ...