Law enforcement agents sometimes find unlawful drugs concealed in vehicles attempting to cross into the United States from Mexico.  The drivers of these vehicles commonly deny knowledge of the drugs, asserting that someone must have placed them in their vehicles without their knowledge.  The government has often prosecuted the drivers for drug-smuggling even if there was no direct evidence refuting the drivers' protestations of ignorance.  The government has typically argued that the drivers' claims were implausible because drug-smugglers would not take the risk of entrusting their valuable products to unknowing couriers -- i.e., "blind mules."  In recent years, however, the government has begun to acknowledge that the use of "blind mules" to smuggle drugs is, in fact, widespread.  The resources listed below illustrate this new awareness: