Here is the news release summarizing the investigation: Investigation Results Made Public in 2012 Grizzly Bear Shooting

From what I see here, it sounds like hikermor's summary was correct. The release states: "Park rangers and science and resource management personnel believe that both the bear spray and bullets contacted the grizzly bear at nearly the same instant."
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Victory awaits him who has everything in order — luck, people call it. Defeat is certain for him who has neglected to take the necessary precautions in time; this is called bad luck. Roald Amundsen