In our last post, we discussed a phenomenon that has attracted national attention. Juan crossed the border almost every day to attend college in the United States. Like many individuals who cross the border regularly, Juan applied for a SENTRI pass.

A SENTRI pass allows people to cross the border faster and with less inspection than other individuals. In order to qualify for a SENTRI pass, individuals must have clean criminal records and complete rigorous interviews, which Juan had done. Unfortunately, his clean record made him a target.

One day when he was going to school, the border patrol stopped Juan, and when they searched his car, they found 50 pounds of marijuana. Juan was arrested and convicted of drug charges.

Throughout his trial, Juan insisted that he was innocent and knew nothing about the drugs. Once he was convicted, his lawyer filed an appeal. After at least five other people had been arrested with circumstances alarmingly similar to Juan's, a judge demanded further investigation.

When the FBI investigated, they uncovered frightening information. As part of a complex and invasive plan, a Mexican drug cartel was planting drugs in the cars of unsuspecting people.

According to the criminal complaint, the drug cartel hired people to monitor the lane used by people who hold SENTRI passes. They recorded the time of day in which motorists drove through, as well as the make, model and color of their cars. The lookouts watched for students and professionals -- people who have consistent routines and would need to cross the border almost every day.

When they identified a target, they followed the car into Mexico, and at night, they approached the car and wrote down its VIN number. They also attached a GPS tracking device on the car, so they could monitor its movements.

The VIN number was brought to a locksmith, and two copies of the car's keys were made. Members of the drug cartel took one copy of the keys to put 50 pounds of marijuana in the car's trunk. The other set of keys was used to open the trunk and retrieve the drugs once they were in the United States.

The plan was simple and effective, but the striking similarities in the cases eventually gave it away. A judge who heard several cases -- and who convicted several people -- caught on. The cases against the people who were wrongly convicted were dismissed, and they were freed.

Unfortunately, being freed doesn't given them back the months in which they were imprisoned, and it will be tough for them to shake the knowledge that someone invaded so much of their privacy without their knowledge.

Source: CNN, "'Blind mules' unknowingly ferry drugs across the U.S.-Mexico border," Emily Smith, Jan. 24, 2012