Community policing promotes the implementation of bi-directional collaboration channels between citizens and Law Enforcement Agencies (LEAs). By enhancing the discovery of relevant and up to date information, it speeds up the detection of risks, eases their prevention and builds a continuum of collaboration which motivates citizens and LEAs to work together. Over 36 months, TRILLION - TRusted, CItizen - LEA coILaboratIon over sOcial Networks - delivers a fully-fledged platform to support the extensive collaboration between citizens and LEAs. The operational environment of the platform is not limited to an on-going crisis, but also extends to the period before it through early identification and prevention of emerging risks. Major challenges addressed by TRILLION include creating the necessary trust to entice provision of information, ensuring that the information leads to realistic and credible knowledge and using this knowledge through secure bi-directional communications to guide actions of individuals closest to an identified risky situation. TRILLION delivers a comprehensive service based platform and mobile applications that support the knowledge-based, real-time collaboration among law enforcement agents, first responders and citizens whilst ensuring that privacy and data protection are taken into account. The TRILLION consortium and supporting organisations include 6 citizen communities, 6 law enforcement stakeholders, 3 industrial players and 5 universities and research centres. Extensive trials take place through pilots, early validations and serious game based training across Italy, Portugal, Sweden, the Netherlands and the United Kingdom, involving close to 2.000 citizens and law enforcement agencies representatives.