He was gunned down after trying to wrestle the officers firearm away from him inside the cruiser. Then fled, Once the officer got himself together he told Brown to stop, at which point brown turned and ran towards the officer. The officer had no other option then to drop his attacker.
None of what you say is fact, only untested assertion.
It may be the officer's account, when and if he testifies under oath, but no one has any account that's anything like that trustworthy. So far, the only indisputable facts are that Brown was gunned down and died in the street.