Amaral must have known that would be the case...imo..
So if he really suspected them why did he write a book that would prevent a prosecution...it makes no sense...imo
I think if he ever really did suspect the McCanns the forensic reports must have crystallised the realisation that he had wasted months following entirely the wrong leads.
I think there may be a tendency to consider Madeleine's case in isolation; ignoring the background material which may have been an influence in how it was perceived and the haste in which it was thought necessary to 'solve' it.
Portugal was still smarting from the Casa Pia child abuse scandal and although the British press seemed ignorant of it at the time (judicial secrecy?) the residue from the Cipriano case must in my opinion, have played a role in the thinking of those in the know.
None more so than Goncalo Amaral who was an arguido.
Taking all the factors into account, I think there may be a story to tell were the information academically researched. Whether Netflix are the ones to do that remains to be seen although I believe they have researchers in the field working Madeleine's case. Having read about their treatment of JonBenét's case I doubt anything other than sensationalism and profit is the motivation.