People who have been in the military will know that if they are interned as combatants and questioned, all they have to answer is their name, rank, and serial number. So for example, if Private Paula is taken captive with his unit of Marines, he will repeat again and again, "I am Private Paula, 111111-P-123456" but cannot be made to answer any other question through bad treatment (though better treatment for answering is ok). Also often answering might violate other orders by their superiors.
Now, let's assume for some reason or another, PP ends up captive in the US during a mission that considers the private a hostile combatant - for example during a training exercise that declares the private to be a member of the Moronian military which attacks the training area. However, the captor is the (civil) police, who begin to question them about a crime that simultaneously happened and in which the private might or might not have been involved. In any case: PP doesn't put up resistance, is read their rights and all such, but all they answer is their name, rank, and serial number before being carted to the station. Let's for simplicity assume that the whole thing happened in Nevada.
Now, here the rest of Article 5 of the Geneva convention comes into play:
No physical or mental torture, nor any other form of coercion, may be inflicted on prisoners of war to secure from them information of any kind whatever. Prisoners of war who refuse to answer may not be threatened, insulted, or exposed to any unpleasant or disadvantageous treatment of any kind. - Article 17 Geneva III Convention (1949)
The private was arrested in some way or another, but does the private count as interned in such a way that they can rely on the Geneva Convention?