noun
missing person; unidentified person
Abbreviation of terms like 行方不明者 (missing person) or 身元不明者 (unidentified person). Used in news, police reports, and formal contexts.
See also: 行方不明者 · 身元不明者 (みもとふめいしゃ)
警察は不明者の捜索を続けている。
The police are continuing the search for the missing person.
事故現場で身元不明者が見つかった。
An unidentified person was found at the accident site.
Explicitly means 'unidentified person' (identity unknown). 不明者 can cover this meaning as well, but is less specific.
Abbreviation formed from 不明 (unknown) + 者 (person). The exact historical derivation is uncertain, but it likely arose in bureaucratic or journalistic contexts.