We ran across some interesting declassified POW/MIA documents posted online in June 2015 by the CIA (having been released to a FOIA requester earlier).
Hanoi made it clear as early as 1969 that the return of US POWs would be linked to payment of war reparations by the US, recounts a then-Top Secret White House history of the issue from 1985. It summarizes POW/MIA negotiations during previous Administrations and the linkage of those reparations, secretly promised by the Nixon Administration in 1973, to the return and accounting for American POW/MIAs by Vietnam (for greater detail on this link, including a tragi-comic secret meeting in which the Vietnamese traded an incomplete list of POWs for an American promise of aid, see Lynn O'Shea's excellent book here.)
Excerpts of that secret White House history are at bottom, along with a copy of the full text. Immediately below is a declassified 1973 US intelligence report describing the "ridiculously low" percentage of POW/MIAs from Laos accounted for in the process leading up to that ultimately failed attempt to swap American cash for a full POW/MIA accounting. For a haunting and infuriating history of one of the missing American heroes referenced in this report, see Jeffrey Donahue's site on his family's hunt in Laos for Air Force officer Morgan Donahue, The Search for Morgan Jefferson Donahue.
Worth noting as you review these long-secret records is that the US government is still withholding 60-year-old + POW/MIA documents from the Korean War (our focus) along with many others from Vietnam. [Bethesda, 7/25/15]