Are you confusing the term 'prisoner' with 'criminal'? Prisoner is used to refer to people waiting for trial frequently, and dictionaries seem to support this definition.

Well we can mince words, but functionally you are deprived of your freedom while being presumed innocent if the government decides it so.

Perhaps you have a different term besides "prisoner" to describe someone who is imprisoned before their trial rather than after. But the parent comment is correct: whatever you call them, these people are not afforded all of the rights that the rest of us have.