ds said:
A captured unit (white unarmed counter) is 'abandoned' in the RPh.
The releasing unit then fires/kills the unarmed unit in the subsequent PFPh.
Does this action invoke any form of Massacre/No Quarter?
Since you abandoned the unit in the RPh and fired upon it in the subsequent PFPh, the unit is still in the same Location as its former captors. Per A20.4, "Only SS, Japanese, Partisan, Russian, or berserk Infantry/Cavalry - if not in Melee - may eliminate an unarmed unit in their Location not in the act of escape." Since the rule doesn't say anything about actually guarding that unarmed unit, I'd say this would apply in your situation, with the appropriate restrictions on who can fire and the subsequent penalties under A20.4 and A20.3.
However, if not in the same Location (say another squad elsewhere is firing on your just-abandoned unarmed unit), I can't right off hand find anything that says you'd suffer these penalties.
Pete