I don't think you can prosecute someone without fingernails as that is proof that you tortured them. I just finished watching "Unthinkable" and they said it in the movie....I think it makes sense.
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It depends on the circumstances. If the fingernails are missing by natural causes, then obviously they are held to the same laws as everyone else. If the person has been tortured, and the fingernails are removed as a result then this person would be released for inhuman treatment; this applies to all forms of physical torture.