After Castile’s death, I wrote a piece for MIT Technology Review about “sousveillance,” the idea posited by the inventor Steve Mann, the “father of wearable computing,” that connected cameras controlled by citizens could be used to hold power accountable. Even though bystander video of Eric Garner being choked to death by New York police officer Daniel Pantaleo in 2014 had led not to Pantaleo’s indictment but to the arrest of Ramsey Orta, the man who filmed the murder, I offered my hope that “the ubiquity of cell-phone cameras combined with video streaming services like Periscope, YouTube, and Facebook Live has set the stage for citizens to hold the police responsible for excessive use of force.” I was wrong.