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Today Carlos had advised me not to answer any of the questions put to me. He explained that this was my right as an arguida and it was the safest option: any responses I gave might unintentionally implicate me in some way.
He knew the system better than I ever would, so it struck me as prudent to accept his guidance.
Since I was unable to comprehend how anything I’d said already could have led me to this point, I wasn’t about to try to get through to the police again now. Kate McCann
She acted on legal advice and having spent many hours being interrogated on the previous day knew that the police just weren't listening to what she had to say or they would not have made her arguida.
I think she was well aware of the ramifications. She would know that Joana Cipriano's mother was in jail and that no-one was looking for Joana who was the last missing child case Amaral had worked.
Oh dear, where to start?
She wasn't 'interrogated', she was questioned as a witness. Regarding events that would not incriminate her.
As to why she was made an arguida the next day. When one is asked questions that might lead to incrimination, Portugal requires that one is made an arguido, as it confers rights and freedoms not open to a witness. Notice the word 'might'. 7 arguidos on, and not one has been charged with anything.
If you have any information that Kate was aware of the Cipriano case, this would be a good time to reveal it. I do not recall Kate making such a claim. If you don't it is pure speculation.