Firstly, Greater St. Louis is much more vast that you probably imagine. It includes places well outside of the city. For perspective, the city of St. Louis has a population of just over 300,000. But the GSL area has a population approaching 3 million. It's a big difference. No sources, cited on Wikipedia or otherwise, cite murder rates that high for the city of St. Louis. This may simply boil down to a reading error on your part, which is understandable given your unfamiliarity with the area.
But, while I do agree that civilian-on-civilian homicide is much more common: this should not be debated by anyone. If it weren't, it would mean we're living in a horrible, militant police state. However, that statistical regularity does not minimize this instance and those cases of civilian homicide do not carry the representation of a systemic social problem in as obvious a way as this one does.
Lastly, I cannot cite a specific number because those figures do not exist, at least not in any form that I am comfortable using as a source. If I find a figure I'm comfortable with, I'll quote you in this thread, but, as you said, it's a hard phenomenon to quantify. However, undoubtedly, your unsupported assumption that this is the only time an officer has shot a civilian is not accurate. It's almost a matter of common sense. I don't expect you to pay attention to the St. Louis-area news to be able to deduce that more than one police-on-civilian homicide happens in an urban area in a given year. To support this, in a more anecdotal sense, I cited the incident that happened yesterday, where another (at this point unnamed) black teenager was fatally shot. From what I understand, he was armed and the decision to use lethal force was correct. But it still just supports what is kind of obvious.
Also, either you misread my "narrow-minded" statement or you are getting overly defensive. I did not call you narrow-minded: I said the premise that the unruliness of the black community is the sole (or even one of the most important) factor in their current social plights is narrow-minded. Which it objectively is.