CSgt Blackman was convicted on his own words: he knew at the time that he was committing a crime. He didn't subsequently have his conviction quashed: it was reduced to manslaughter in recognition that his actions were not those of someone in full control of their faculties: i.e.diminished responsibility.
Not the actions of someone who carried enemy weapons to leave as 'supporting evidence' then? Neither did he push junior soldiers to kill prisoners and 'blood' them. (And that's a metaphor for locking them in, imo.)
Not really the same.
CG