How would society react to “the Watcher,” a technology capable of efficiently, unerringly, and immediately reporting the perpetrator of virtually every crime? This Essay treats that speculative question as an opportunity to explore the relationship between governmental surveillance and criminal justice. The resulting argument is unabashedly fictional but draws attention to pressures that may influence the real world. For instance, the Watcher casts doubt on perfect surveillance’s ability to improve the law, supports judicial attentiveness to substantive law when reviewing rules of investigation, and suggests that legislative control might displace prosecutorial discretion. The Watcher also draws attention to the relationship between surveillance and regulatory intricacy, as well as to ways of preserving human mercy within automated criminal justice.