Giving the 3 Burglars a months prior warning they are going to nick them is obviously not deemed damaging to the investigation.
So would it really be damaging to show us the evidence which clears the McCanns, or could it actually assist the search for Madeleine ?
Reading between the lines on this one I don't think there is any evidence to clear them, how do you prove a negative. If they had evidence to support the suspicion that both of them were complicit in Madeleine's disappearance then I am sure Snr Amaral would have acted a lot faster than he did. And if not him, then his colleagues.
Also people who are insisting with great force that they have not been cleared, well yes they have. Again facts are that the Grange team do not consider Madeleine's parents as suspects. I’m fairly sure they must have explored the possibility that they could have been involved and as such, ruled it out.
In fact if some need to see it in writing, then most of the news sites carried a direct quote from Redwood explaining that the McCanns were not under suspicion nor linked to any of their ongoing leads after reviewing the evidence. Seems that some prefer to deal with semantics when it comes to interpreting the posture of a DCI when he says someone is no longer under suspicion of a crime.