An investigation assist device is connected to cameras installed at a plurality of intersections respectively. The investigation assist device has a processor and a storage that records road map information including the plurality of intersections and captured video of each camera in association with camera information and intersection information. The processor extracts camera information of intersections adjacent to a first point where an event occurred according to an information input including information on the first point and feature information of a vehicle having caused the event. The processor retrieves a vehicle satisfying the feature information of the vehicle using a captured video of a camera specified by the extracted camera information. The processor analyzes feature information of the retrieved vehicle. The processor updates feature information of the vehicle by adding the analyzed feature information of the vehicle to the feature information of the vehicle input by the information input, and stores the updated information in the storage. The processor updates detection point information of the vehicle from the information on the first point into detection point information of the retrieved vehicle, and stores the updated information in the storage.