There was also disagreement between the Blackwater guards - there were 4 vehicles and I believe only 2 were firing.
Prosecution also tried to discredit State Department investigation findings at trial saying they were part of a coverup while relying on FBI investigation that happened weeks later.
Defense argued that there was a coverup by US and Iraqi investigators of hostile fire.
Radio logs showed them reporting hostile fire from insurgents as well as Iraqi police throughout.
Insurgents frequently dressed as Iraqi police.
Honestly I would have a very difficult time with any prosecution where there is clear evidence of hostile fire (bullets, radio logs, pictures of damaged vehicle).
Even if there were one or more orders disobeyed during the incident.