Back in the day when I was a young street cop, a robbery at a convenience store would set off the usual chain of events. I’d arrive on scene, talk to the shaken clerk and any so-called witnesses, and they’d give me the vaguest description imaginable: “male, maybe 5’10”, dark hoodie, ran that way.” That was all we needed. We’d hit the streets, looking for someone who looked like they didn’t belong. Soon enough, we’d find our usual suspect—a guy with priors who happened to be in the wrong place at the wrong time. He’d get stuffed into the back seat of a patrol car, hands cuffed behind his back, and paraded back to the crime scene. The victim and witnesses would take a glance and, pressured by the moment and their misplaced faith in police instinct, they’d nod. “Yeah… that’s him.” Case closed. The jury would hear that the witnesses “positively identified” the suspect, and the court system would grind ahead like a machine with no brakes. Only one problem: this time, the guy was complete...