farmerj wrote:neg·li·gent (ngl-jnt) wrote:adj.
1. Characterized by or inclined to neglect, especially habitually.
2. Characterized by careless ease or informality; casual.
3. Law Guilty of negligence.
Sorry, I see no evidence of any items in the definition you supplied. The story only mentions while retrieving his weapon he pulled the trigger while he was getting out of the car, in a tense situation. I don't think there is anything else, unless I missed something, or there is furthur information in another article I didn't read.
For the above meaning to apply here, it would have to be known the officer routinely lets his finger drift into the trigger guard, espeically while retrieving it from his holster. And to make it even more plain, it would be helpful if he had a history of unintentially firing his weapon. Perhaps he's had additional training to relieve this problem and failed his class? But I don't see any of that. Just a single incident in a tense situation.
I just don't think one accident with no backup history is enough to call it negligence according to your definition. I think the cop simply fired his weapon in error. That to me is accidental.