The decision was not made by Comey. Comey knew DOJ would not prosecute. Comey either did what he was told or went along with the obvious situation.
The decision was made by Obama and Lynch.
That didn't matter as Lynch already said she would prosecute if FBI recommended it - ball was in Comey's court (so to speak)
"Comey either did what he was told..."
Yes, that is much more probable. Senator McCarthy knew the charges he was throwing out would destroy his career - but he did it anyway.
Comey is a gutless, spineless hack who sold (what was left of) his soul to the devil yesterday.