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If you've ever fired either a Glock 9mm or a submachine gun you will know how difficult it is to hit a small target, especially one that is moving, presumably fast - especially if you don't have time to brace against the recoil. Aiming for a leg is less likely to succeed than firing into the torso, and therefore more dangerous to both the shooter and any unfortunate passers-by behind the target.
Looking at the pictures of him on the stretcher it appears he was shot in the stomach, which indicates the officer went for the largest target.
Why didn't they shoot to injure/disarm?
Convenient for the terror narrative that he was shot and killed and now we'll never know his motives