An investigation assist device is connected to cameras installed at a plurality of intersections respectively so as to communicate with the cameras. The investigation assist device includes a processor and a storage that records road map information including the plurality of intersections and captured video of each of the cameras in association with camera information and intersection information. The processor retrieves a vehicle using the captured video of each of the cameras installed at one or more intersections within a predetermined distance range from the intersection where the event has occurred, based on input information including date and time information when the event has occurred, the intersection information where the event has occurred, and the feature information of the vehicle having caused the event, the captured videos corresponding to the date and time information. The processor updates the detection date and time information of the vehicle from reception date and time information on a report indicating an occurrence of the event to detection date and time information of the vehicle, updates detection point information of the vehicle from the intersection information on the intersection where the event has occurred to intersection information on another intersection where the vehicle is detected, and stores the updated information in the storage.