Here are some articles to get you started.
https://www.aclu.org/blog/privacy-technology/surveillance-te...
https://www.telegraph.co.uk/news/worldnews/northamerica/1209...
https://www.washingtonpost.com/local/public-safety/the-new-w...
National data from intelligence agencies are provided to municipal police through "fusion centers". Different cities provide their own data into these centers (e.g. Seattle recently built and tore down a city-wide camera surveillance system) which are consumed in the other direction. Threat scoring software use various data feeds including those from social media platforms.