Over three decades ago, at the height of the war on drugs, the government began practicing asset forfeiture. Basically, a police officer can take money or property from you, even if you've never been charged with a crime, and it's up to you to prove that you legally acquired it. Since 9/11, a rise in aggressive policing has led to hundreds of millions being seized on America's roads from motorists who have never been charged with a crime. And cash-strapped law enforcement departments are reliant on that cash for funding.
From the story: "A thriving subculture of road officers on the network now competes to see who can seize the most cash and contraband, describing their exploits in the network’s chat rooms and sharing “trophy shots” of money and drugs. Some police advocate highway interdiction as a way of raising revenue for cash-strapped municipalities." Read the full investigation at the Washington Post