Do you want to know the dirty secret about how the Drug Enforcement Administration (DEA) confiscates suspected drug traffickers' money? The truth is, it's not hard: Agents just go to an airport and wait for cash to drop into their laps.

A March report by the Justice Department's inspector general (I.G.) found the DEA seized a whopping $4 billion in cash over the past decade using civil asset forfeiture, mostly from airports, train stations, and bus terminals.

Contrary to DEA rhetoric, these seizures have little to do with ongoing criminal investigations and everything to do with bringing in money. In 81 percent of the cases the I.G. reviewed, there were no accompanying criminal charges.

A 2016 investigation by USA Today found the DEA regularly mines American citizens' travel information and relies on a network of confidential informants in the travel industry, who often get kickbacks for snooping on suspicious passengers.

Common red flags include buying a ticket within 24 hours of travel, buying a ticket for a long flight with an immediate return, buying a one-way ticket, and traveling without checked luggage. They also include traveling to or from "a known source city for drug trafficking," which in practice can mean just about any major city in the United States.

The DEA detains suspicious passengers, questions them, and searches their luggage. If agents find large amounts of cash and think it's linked to drugs, they seize it—even if there is no hard evidence that it is connected to illegal activity. As the I.G. notes, agents "rely on their immediate, on-the-spot judgment." The passenger is then often released, bereft of money.

Many of these seizures are well over $100,000, but in some cases this "on-the-spot judgment" leads agents to seize smaller amounts of cash while failing to do any basic investigation. In 2014, agents at Detroit Metro Airport took roughly $25,000 from Christelle Tillerson after she was flagged for buying a one-way ticket to Los Angeles. According to the Detroit Free Press, Tillerson said the money was from her boyfriend's retirement account, and she was using it to buy a truck. She was never charged with a crime, and her lawyer said the DEA agents never even questioned her about drug trafficking.

Tillerson sued, and eventually the government gave back all of her money—except for $4,000. One wonders how the Justice Department determined that amount was likely connected to illicit activity while the other $21,000 was not.

In another case highlighted by the inspector general report, the DEA seized $27,000 from a man in an airport but let him keep $1,000 to travel home. If the task force agents really thought that man's cash was connected to drug activity, why allow him to keep any of it? If they weren't sure, why take it in the first place?

There is no logical reason. Without clear evidentiary standards or guidelines—or even the convincing appearance of an ongoing criminal investigation—the DEA's asset forfeiture program becomes little more than a poorly disguised shakedown.

"When seizure and administrative forfeitures do not ultimately advance an investigation or prosecution, law enforcement creates the appearance, and risks the reality, that it is more interested in seizing and forfeiting cash than advancing an investigation or prosecution," the inspector general warned.

That reality is already here, and federal law enforcement officers are raking in hundreds of millions of dollars a year with little oversight or constitutional protections for property owners.

Most of these types of seizures are never challenged. The I.G. found petitions were filed in only 20 percent of the DEA cash seizures it reviewed. Of those that were challenged, though, 40 percent saw money fully or partially returned to the owner, indicating that there may be a significant number of unfounded seizures going unchallenged.

Darpana Sheth, an attorney for the libertarian nonprofit law firm the Institute for Justice, said in a statement that the I.G. report's findings "fundamentally undercut law enforcement's claim that civil forfeiture is a vital crime-fighting tool."

"Americans are already outraged at the Justice Department's aggressive use of civil forfeiture, which has mushroomed into a multibillion dollar program in the last decade," she continued. "This report only further confirms what we have been saying all along: Forfeiture laws create perverse financial incentives to seize property without judicial oversight and violate due process."