###### Abstract  
Preventing terrorist attacks at soft targets has become a priority for our society. The realization of sensor systems for automatic threat detection in crowded spaces, such as airports and metro stations, is challenged by the limited sensing coverage capability of the devices in place due to the variety of dangerous materials, to the scanning rate of the devices, and to the detection area covered. In this context, effectiveness of the physical configuration of the system based on the detectors used, the coordination of the sensor data collection, and the real time data analysis for threat identification and localization to enable timely reactions by the security guards are essential requirements for such integrated sensor-based applications. This paper describes a modular distributed architecture of a command-and-control software, which is independent from the specific detectors and where sensor data fusion is supported by two intelligent video systems. Furthermore, the system installation can be replicated at different locations of a public space. Person tracking and later re-identification in a separate area, and tracking hand-over between different video components, provide the command-and-control with localization information of threats to timely activate alarm management and support the activity of subsequent detectors. The architecture has been implemented for the NATO-funded DEXTER program and has been successfully tested in a big city trial at a metro station in Rome both when integrated with two real detectors of weapons and explosives and as a stand-alone system. The discussion focuses on the software functions of the command-and-control and on the flexibility and re-use of the system in wider settings. command and control; sensor data fusion; re-identification; position prediction; threat detection; public security 28 January 2023 Revised: 14 February 2023 Revised: 1 March 2023 Revised: 3 March 2023 Revised: 1 March 20  
smart city applications [5], allow one to conceive novel early threat detection systems that activate alarm management processes. The function of the command-and-control (C&C) software in such a system is the orchestration of the plurality of sensors, deployed in various delimited areas of a public space and targeting potential terroristic persons, e.g., wearing explosive objects hidden under clothes or inside bags. The technological challenge is twofold: to optimize the work of agents on field by providing security checks in a non-intrusive manner and to support localization of the threat in the crowd; also, the second challenge is to strengthen the operations at the security control room of a critical infrastructure through automatic communication of alarms and of any relevant information for the police. The first challenge requires one to integrate and fuse detections of different sensors that produce data in real time and that work unnoticeable to the persons passing through the observed locations. The second requires a robust real time system for automatic alert generation without impacting the passengers' flow, and which can innovate existing situational awareness systems devoted to public security. Indeed, the control work in security rooms currently is mostly based on direct observation by the operators through the video cameras deployed at different sites of the infrastructure, and alarm communication and management are very much human-based processes. This paper describes a modular distributed architecture of a command-and-control software, which is independent from the specific detectors and where sensor data fusion is supported by two intelligent video systems. One allows re-identification and tracking of a person previously identified by another camera, and the other delivers position prediction of a person near a sensor to reduce detection misses.