Harrison formed no pre-conceived ideas (of his own). Good detectives don't. They analyse the facts and draw their own conclusions.
Harrison's hands were tied by a brief (handed to him by the PJ) to investigate that Madeleine had been murdered and did so.
Amaral either lied or was incompetent when he said no one talked about murder.
And certainly (by English libel law) he libelled the McCanns with that reference.
No clue about Portuguese libel law.
I would like to know if you have a cite for the bolded bit? I can't find it in his book.
The request for Harrison's help was made to the NPIA on 20th July by Encarnacao. Harrison says the request mentioned murder. There is no copy of that request in the files, so it can't be checked.
Harrison would have talked about murder because that was his brief; to look for a murder victim. If Amaral hadn't seen Encarnacao's request he may well have concluded that murder was being suggested by Harrison.
It seems that Encarnacao was operating outside the files, as he did with the unrecorded interview with the McCanns on 8th August.
Amaral has been subjected to unrelenting criticism but Encarnacao and Neves seem to have been following an unrecorded agenda of their own which didn't help the investigation at all. Neves played down his contact with the McCanns, but he and Encarnacao met with them on a regular basis at the British Consulate. Had this arrangement not been in place then Amaral may have met and spoken to them at some point, but he was excluded by his superiors.
The final meeting took place at the Police Station, was unrecorded and should not have happened without arguido status for the McCanns. Not only that, if the parents were involved they were given advance warning about the direction of the investigation and another month to prepare themselves before the officially recorded investigation, following procedure, did make them arguidos.