Imo it can be considered "suspicious" if there is a mountain of evidence against a suspect which points to their guilt and they refuse to explain any of it .
As for the McCanns I thought at the time how ridiculous it was that they were arrested and made suspects.
In my opinion the right to silence is a protection for the innocent. Everyone is innocent until there is evidence against them which can be proved in a court of law.
In my opinion it is not for a suspect to 'explain' anything allegedly 'pointing to their guilt' ... it is the job of the police to gather evidence to substantiate any 'mountain of evidence' they may think are pointers to guilt.
As we have seen from the questions asked of Kate at the arguida interrogation ... the police simply did not understand the forensics they thought pointed to Kate's guilt ... all they had to do to rectify that would have bee to check it out with their own forensic experts.
Which I believe is precisely one of the diligences carried out by the Rebelo investigation who sent a four strong team of experts, including Francisco Corte-Real, vice-president of Portugal's forensic crime service to Britain to confer with the British experts.
https://www.yorkshirepost.co.uk/news/forensic-experts-discuss-dna-samples-in-madeleine-inquiry-1-2477684Therefore I think your initial reaction to Kate and Gerry being made arguidos was about right, although it is worth bearing in mind that they were never arrested.
As is obvious from the PJ Final Report
all things having been considered there was no further questioning of Kate or Gerry nor charges laid against them. The Rebelo investigation having checked out the forensics in what was initially thought to have been grounds to make them arguidos in the first place proving groundless when looked at closely by experts.
Fully vindicating Kate taking her lawyer's advice not to answer the questions put to her as arguida. Forcing the police to investigate further, albeit with another coordinator in place, and finding no evidence against her.
