Nonperson
A nonperson is a citizen or a member of a group who lacks, loses, or is forcibly denied social or legal status, especially basic human rights, or who effectively ceases to have a record of their existence within a society (damnatio memoriae), from a point of view of traceability, documentation, or existence. The term also refers to people whose death is unverifiable and about which inquiries result in a "blank wall" of "nobody knows".
Ways to become
Some common ways in which people become nonpersons are:
Never having been sufficiently documented as existing
Loss or deletion of the trail of documentation so that the specific person can no longer easily be linked to a documentary record or cannot be shown officially to have existed
Covert abduction by government or other bodies combined with plausible deniability
Long-term absence or other circumstances leading to an incorrect belief and legal documentation that they have died
Death, when it is unverifiable and left as an open case as to what happened