This is, I believe, the relevant section (chapter 15) in The Truth of the Lie:
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In order to conceal his crime, the murderer can hide the body, or alter the crime scene in such a way as to divert suspicion. But this is not always the case. Someone may also get rid of a body without having committed a criminal act. For what reasons? Fear, for example, of being judged by his peers.
Imagine a couple of doctors going on holiday abroad, to a country they hardly know. They leave their three children to sleep alone in their apartment to go to a restaurant, a hundred metres away. When they come back, one of the children is dead. It could be an accident or murder. What do they do? They call the police and, in a way, admit that they were more than negligent. And what will happen when they go back home? What will the consequences be? Will their professional future be compromised? Will they be charged? Will they retain custody of the younger ones?
As I said at the start of the book, no lead must be abandoned while it has not technically been ruled out.
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Mr Amaral is merely pointing out various possibilities. I do not see any reason he is promoting "Death by Calpol" as being his hypothesis.
For instance, he is pointing out that "Someone may also get rid of a body" even though they did not commit a criminal act.
I have no idea what happened, but Mr Amaral is, on my interpretation, stating that MBM could have died in an accident or been murdered.
A murder would involve a third party, but there is no guarantee that the murderer moved the body. Another third party could have moved the body.
MBM could have died in a 'hit and run' and, again, another third party could have moved the body.
It seems to me to be fair game to scrutinise his theories, but I do not believe that he has limited himself to one particular theory as there is no strong evidence as to what happened.
He does appear to be giving weight to the 'intelligence' from the dog alert in the apartment, which in his view indicates that either MBM died in the apartment or her body was temporarily moved to the apartment.
AFAIK there is no evidence at present to implicate any third party, and it is my understanding that no third party (especially the parents) are currently suspects.
Abduction is another valid theory.
Mr Amaral states:
At a certain stage in the investigation, to explain Madeleine's disappearance, we had considered the scenario of the concealment of a body. But before coming to that conclusion, we had to exhaust all leads that favoured the theory of abduction.
They are all theories (of course, not all theories are created equal). At present SY are trying to determine what happened to MBM. I hope they are successful.