'Unrequited' shows a group of former special forces who rescued a tortured American Prisoner of War who then goes on a killing spree of officers who certified that all POW's were exchanged.
Are there actual discrepancies between POW's taken and those returned?
See my earlier answer here: https://www.reddit.com/r/AskHistorians/comments/l88o0f/were_there_any_verified_american_pows_who_were/
There is no evidence any US prisoners were held in Vietnam after 1973, it is a false conspiracy theory.