Amaral gets the blame because he stuck his head up above the parapet but you are correct, the decision to designate Murat and the parents as arguidos was a joint decision by many others including the English police. That said, Amaral's input would have been crucial however and could not have happened without his agreement and the agreement of the PJ team under his control.
If we look at the Bamber case, a very senior officer was moved sideways when he disagreed with the investigating team below him, this isn't anything new and occurs regularly in investigations. Had Amaral not had the unequivocable support of those below him and of his bosses he could not have made the three suspects arguidos. And we all know what happened when that support melted away.
If I had had anything to do with it, based solely on the information contained in the Policia Judiciaria case against him ...
http://www.mccannpjfiles.co.uk/PJ/ROBERT-MURAT.htm ... I would have felt fully justified in making Robert Murat an arguido and prime suspect.
Indeed, one wonders if the McCanns had packed their bags and headed back across the channel at that point, if he might not have been charged and brought to trial.
In my opinion there is no comparison between the justification for the three parties being made arguidos.
The fact that they are all three innocent and walking free probably shows that in cases involving high profile individuals such as these three the burden of proof enabling charges to be laid in Portuguese law must be seen to be being applied.
Murat has briefly detailed the devastating and lasting effect the suspicions engendered by his arguido status had on his life. I don't think the McCanns fared any better, but in their case I think that outcome was calculated.