The Safe-Neighborhood App

One of the best ways to maintain some level of security in one's neighborhood is by fostering a community of alert citizens. Simply being alert to the presence of some danger is not enough, however. Citizens must also be able to share what they are observing with others, especially with law enforcement. This app is a social-networking smart phone application that offers a platform for sharing this important information. Citizens are able to join their neighborhood group on the app, and they'll be able to share information about dangers they perceive in their neighborhood and discuss ongoing safety issues. The app will also give law enforcement access to this information, which they can then put to use in apprehending a criminal or perhaps prosecuting a case.  Thus, this application offers the potential to significantly increase levels of safety. It also raises some important privacy concerns. In addition to the question of the legal permissibility of allowing law enforcement to have access to the messages that are exchanged on the app, there is a worry that certain overzealous users may implicate someone in wrongdoing, even where there isn't any.  How can the features of the application be developed in a responsible way?  How can the use of the app by law enforcement be designed in order to strike a balance between privacy and security?