What the actual planning was we may never know....
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An interesting parallel with your theory about using Stevens as a ransom item.
The Iran/Contra situation was based on helping anti-communists in Central America with money obtained by selling arms to Iranians.
Today, it is possible that Stevens was very involved in getting arms to Syrian anti-Assad fighters.
The only thing that is consistent about this story is that it remains inconsistent. What I thought I knew yesterday I don’t know today.Never saw a story with so many twists and turns! Almost near impossible to follow.