Imagine for a moment that you are the commander of a national counternarcotics team and you receive information that in the next 24 hours a lorry will be loaded with 80kg of heroin, driven across a continent through several countries to arrive finally in your city where the drugs will be repackaged and distributed nationwide. You know that if the heroin is seized at the point of loading, you will net the 80kg and the driver and, perhaps, a few others. This might be a quick win for seizure statistics, but it will make little impact on the overall flow and supply of illicit drugs. A far more effective, but riskier, option would be to allow the lorry to travel to its destination as planned and to monitor the journey, identifying with whom it comes into contact and to whom it finally delivers. In that way, you will have the chance to wind up a complete network and prevent it from doing any more harm.