Citizen event reporting (CER) attempts to leverage the eyes and ears of a large population of citizen sensors to increase the amount of information available to decision makers. When deployed in an environment that includes hostile elements, foes can exploit the system to exert indirect control over the response infrastructure. We use an agent-based model to relate the utility of responses to population composition, citizen behavior, and decision strategy, and measure the result in terms of a force multiplier. We show (...) that CER can lead to positive force multipliers even with a majority of hostile elements in the population. When reporter identity is known, a reputation system that keeps track of trustworthy reporters can further increase the force multipliers. (shrink)