How They’ll Know a Crime Is Taking Place

Devices designed to detect questionable activity are proliferating. Several cities have recently put in place networks of microphone-based gunshot sensors, and others are likely to adopt similar systems. When a sensor picks up a suspicious noise, a computer program analyzes the sound and, if it resembles gunfire, determines its point of origin to within a few yards. A human reviews the report and, if warranted, dispatches officers to the scene—all within about 40 seconds of the gunshot. Meanwhile, a Vancouver company is testing marijuana breathalyzers that can approximate the amount of THC in a person’s system; Guohua Li, an epidemiologist at Columbia University, thinks they will probably be in routine use within five years. Police may also start making use of intelligent surveillance cameras equipped with sensors that can identify abnormal or suspicious behavior. According to Jennifer Lynch of the Electronic Frontier Foundation, such technology is being tested in several American cities and is already sophisticated enough to “notice” when someone leaves a bag unattended, or when a car repeatedly circles the same block.

At the federal level, an initiative called Next Generation 911 will enable victims and witnesses to send texts and, eventually, photos and videos to emergency dispatchers—something that’s currently impossible because the 911 network runs on analog technology from the 1970s. People caught in situations—home invasions, for instance, or domestic-violence incidents—in which they can’t safely speak into a phone will be able to get help, and police will receive valuable real-time crime-scene footage.

Controversially, police departments are starting to monitor social media, which many gangs have embraced as a vehicle for branding and boasting. By searching for specific keywords and mapping interactions among individual users, law-enforcement agencies can keep track of suspected gang members, and identify bubbling gang rivalries. They can also infiltrate networks by posting under aliases and “friending” suspects. The Yale criminologist Andrew Papachristos, who works closely with police departments and gangs, says he hopes that the coming years will see a public debate about how aggressively law-enforcement agencies should use the Web to gather intelligence on people who are not already criminal suspects. Many states have set legal thresholds for classifying someone as a gang member, Papachristos says. “But if all the evidence you need is a Twitter post that says, ‘I hate the Disciples,’ the bar is changing.”

How They’ll Find Their Suspects

Usually predictive policing refers to feeding reams of city data into a computer and dispatching extra officers to areas that are deemed to be at high risk of future crime. There’s potential, though, for predictive policing to be less passive. See, for instance, the approach taken in Albuquerque, where, according to a report from the Police Executive Research Forum, officers took the established (if controversial) practice of leaving “bait” for would-be thieves to the next level: they planted iPads, cars, and spools of copper wire in areas that were flagged by their predictive software, and then arrested people who tried to steal them.