Remember, using Twitter's data feed for spying and surveillance is a violation of the service's developer agreement. With the list of keywords, the Northern California chapter of the American Civil Liberties Union's evidence suggests that Media Sonar was selling itself as a way to monitor African Americans specifically. One column groups keywords together under a heading named "Mike Brown Related." Mike Brown was the unarmed black teenager shot by a white police officer in Ferguson, Missouri in 2014.

Further documents (PDF) show that the firm pitches itself as a way to "avoid the warrant process when identifying social media accounts for particular individuals."

What's more, the company apparently directed law enforcement officials to not mention the Media Sonar by name in court, instead using "proprietary search engine" or "internet tools" when pressed for information under oath. It's a far cry from issuing cyanide capsules to its customers, but still pretty telling of the company's intent to keep its secrets safe.

This isn't the first time Twitter has done this, and it likely won't be the last organization to mine social media data for policing. This fall, Facebook, Instagram and Twitter cut off access to tracking systems from Geofeedia . We've reached out to Twitter for more information and will update this post should it arrive.