Back in March 2019, a gunman killed 51 people at two mosques in Christchurch, New Zealand, and streamed the whole thing on YouTube. After that event we took a weeklong look at how social media radicalized people to violence, and how a troll becomes a terrorist. Now, nearly two years later and after a violent attack on the U.S. Capitol, there still seems to be some surprise that online speech leads to offline consequences, so I wanted to revisit some of what I heard that week.