The Demon and the Eye in the Sky

A policewoman was murdered in Ciudad Juarez, Mexico. It looked like it would never be solved. But a new technology helped crack the case, giving law enforcement demon-like powers of omniscience.

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A little over a decade ago, in Ciudad Juarez, Mexico, a policewoman pulled out of her driveway on her way to work. As soon as she started driving, two cars that were parked near her house also pulled into traffic. They began following her. Together, they snaked through the city, an unanticipated convoy in one of the most dangerous cities on Earth.

The police officer didn’t know it, but she was being hunted.

A few minutes later, another unmarked car pulled into the road up ahead, nearly causing an accident, and triggering a cascade of brake lights. The policewoman slowed down, her car crawling forward in the line of cars. As she slowed, one of the cars tailing her pulled up alongside her vehicle, rolled down a window, and shot her several times in the head.

There was no CCTV, no witnesses – or at least none willing to speak to the local cops. It appeared that this tragedy would end like so many in Juarez at the time: as an unsolved murder, with no leads, a dead end.

At the time, the city was clocking 300 murders per month. (By contrast, there are usually fewer than 500 murders per year in New York City, which has six times as many people).

If you were a detective investigating that Juarez murder, what you’d want more than anything is a time machine—the ability to go back to the murder, to watch it unfold with remote control precision, to be able to click rewind, play, and fast forward at will.

You’d want to see, in hindsight, where the cars carrying the cartel’s sicarios had come from, to see where they went next, to see everyone who was involved, all in real time. To a detective, omniscience is the dream, a longing to avoid the long hours of flipping through disjointed CCTV footage in the hopes that a little glimpse of a murderer might, somehow, have been captured by happenstance.

But what if I told you that the murder in Juarez was solved with that level of near-omniscience? That detectives, hours after the murder, were able to watch it happen, even though they didn’t have any video. That they could pause the murder, rewind, fast forward – all without any video recordings, as though they had a time machine. That they could watch the cars converge on the scene of the crime, but also figure out where they came from, figure out where they went next, even where they threw away the murder weapon.

The tactics they used to solve this police officer’s murder were so novel and sophisticated that they could be used to take down entire cartels, to track down their safe houses, even to link seemingly separate murders together, with a god-like ability to see the past as clearly as the future.

This isn’t science fiction. It’s a real story, of a powerful technology, and a controversy that follows its use.

So, how did they solve the murder? And how does the story of that gruesome murder in Mexico link to an influential thought experiment produced by a French polymath more than two hundred years ago? The answer, it turns out, matters profoundly for our understanding not just of government ethics, but of understanding how and why change happens in the world—and the question of whether we have free will.