I have always had a problem with the British interpretation of the Portuguese word arguido. It has become widely accepted that it means official suspect but there is much more to it. A better definition would be 'defendant'.
Someone suggested earlier that it is the equivalent in UK terms of being interviewed under caution. Arguidos are certainly cautioned as far as I understand prior to being interviewed and only then can their responses be later used in any trial but not if self-incrimitory.
I think we have to be careful before applying generalities to the term arguido.
The Portuguese wikipedia definition of arguido makes for better understanding.
https://pt.m.wikipedia.org/wiki/Arguido
It also helps to be aware of the procedures associated with being an arguido bearing in mind that a legal system is based on a mandatory sequence of formally documented steps such that in theory, at least, each decision en route from offence to conviction or acquittal, is circumscribed by legal rules.
In Portugal:
It is mandatory to question a person if there is a founded suspicion they have committed a crime. As the objective is to gain the truth questioning may be ordered with a lesser degree of suspicion.
Questioning may be by a Judge, Criminal Police or Public Prosecutor. The defence lawyer must be informed but it is not mandatory for him to be there except in cases of custodial detention.
The arguido is not obliged to answer and the questions asked at the preliminary stage are of little evidential value.
The arguido has the right of silence; under Portuguese law this is not to his detriment.
He may decide to later waive the right to silence subsequently lying for which he cannot be punished.
The arguido may not under any circumstances make statements under oath as deflection against self incrimination.
An arguido must give details of his identity truthfully.
An arguido is not obliged to help the inquiry in anyway.
In those old fashioned things called Libraries one will commonly a find a reference section. If your librarary is big enough it will have a sub-section on law for European and other States with explanations and so on...