Does this reasoning train justify All Cops Are B*stards (ACAB)?

Dr Bennett's analysis is accurate; the reasoning relies heavily on assumptions that are formed and accepted due to bias (the desire to see the police reformed, or abolished in some extreme cases), as well as the emotional nature of these unfortunate recent events. 

If I had to call fallacy here, it'd be Cherry Picking (for isolating instances of bad policing from the entire set), Hasty Generalization (for using the cherry picked the instances of bad policing and drawing a conclusion based on those), Association Fallacy (because of some bad cops, all are tarred with the same brush - all are seen as "bastards") and Overextended Outrage (since this entire line of reasoning engenders hatred towards cops). To go further, one could even add Misleading Vividness, if statistical data regarding police violence is ignored in favour of a few select (and morally upsetting) instances.

Basically, we have a logical fallacy rollercoaster here. 

Conversely, supporters of the police also make fallacious arguments - if the argument instead simply states that police reform is needed to plug the leaks in the system, then bringing up things like "black on black crime" is a Red Herring. Furthermore, unless otherwise stated, it's not always relevant to point out that most are good, and thus this could be a form of Ignoratio elenchi. 

I'd like to see more dialogue between people of differing opinions, rather than first-resort blocking, accusations of ism-of-the-day, and bad faith attacks.

There is quite a bit of poor reasoning here. Let's break this down:

A: There are 1000 good cops and 100 bad cops in a police department.

Pure dichotomous thinking . Reality is far more complex with otherwise good people behaving badly and vice versa based on many situational factors. But for the sake of the argument presented, let's accept this premise.

B: The 100 bad cops are running around doing bad things, but the 1000 good cops don't do anything about it. 

This, too, is almost certainly a characterization of reality and a dangerous use of hyperbole. But again, let's accept this premise for the sake of the argument.

X: Therefore, 1000 good cops end up being 1100 bad cops, and the 1000 cops that did nothing are just as bad as the 100 bad cops committing the actual brutality.

This is the clear use of black and white thinking that puts all cops in one of two categories and makes the murdering cop as guilty ("bad") as the otherwise "good" cops. The conclusion assumes that the cops that do "nothing" a) know about the bad cops b) know what to do about them c) choose not to do anything about them.

If we go as far to even grant a,b, and c above, we are equating this inaction with murder, which is problematic legally and morally. This implies that the inaction is malicious, that is, the "good" cops are supporting the actions of the "bad" cops rather than a more benign possibility such as not wanting to get a colleague fired over an accusation without sufficient evidence.

I wouldn't even call a fallacy here, just say that it is an argument riddled with bad reasoning and assumptions.

On a personal note, I do agree with the idea that police need to "police" themselves better and be far less tolerant of illegal activities within the department as well as excessive use of force. I would never say, however, that all cops are bad because of the several assumptions that need to be made that, especially when taken together, are extremely improbable.

I don't see this as a logical fallacy. It is simply a progression of thought, based on the premise that if you do not act to stop an atrocity when you have the opportunity to do so, you are complicit in the act. That is not an unreasonable assertion, it even has it's own cliche - "If you're not part of the solution, you're part of the problem". It even has support in the legal world - if you see a murder happening, or are a witness to some other crime, and don't at least report it, you may be charged as an accessory. On the other hand, we celebrate it when a citizen volunteers to help a stranger in trouble. It is a cultural fixture.

So, you may disagree with the premise, but it is not a logical fallacy.