In this paper, we report our work on developing and evaluating a prototype system aimed at addressing the information monitoring and sharing challenges in the law enforcement domain. Our system, called COPLINK Agent, is designed to provide automatic information filtering and monitoring functionalities. This system also supports knowledge sharing by proactively identifying officers who are working on the same or similar cases on a real-time basis. To accommodate the mobile needs of law enforcement officers who are constantly in the field, COPLINK Agent can deliver messages through a variety of communications channels including e-mail, pager, and mobile phones. In order to assess the effectiveness of COPLINK Agent, we conducted a pilot user study at the Tucson Police Department. Overall, COPLINK Agent was shown to be an effective tool for improving the effectiveness and efficiency of criminal investigations in crimes such as gang, theft, and fraud.