This is less an issue of biased narrative vs the truth than _your_ values vs BLM values. To BLM, nothing excuses someone who is supposed to protect and serve putting their weight onto someone's neck for nearly ten minutes. Is a stained toxicology report and non-compliance permission to kill? The BLM "narrative" assumes the answer is no. The right-wing "narrative" assumes the answer is yes. This is less a question of reporting and more a question of what is justified.
Thus, the BLM narrative that police violence is excessive is still compelling if you subscribe to the belief that someone placing their knee and weight on a detained person's neck for 8 minutes is excessive, regardless of other circumstances.
Ask yourself if you think the situation could have been resolved differently, without loss of life. If outcome isn't important to you because of a toxicology report, mannerisms, circumstances of arrest, other reason to deny life... then a certain unorganized group of people would like to remind you and many others like you that _black lives matter_.
But alas, to say the leaked body cam footage "destroys the BLM narrative" implies you won't care about reporting at all if you resort to regurgitating clickbait-language.