An investigation assist device includes a processor and a storage that records information on a road map including a plurality of intersections and captured videos of a plurality of cameras in correlation with a capturing time, camera information, and intersection information. The processor retrieves at least one vehicle satisfying a retrieval condition and extracts a traveling direction of the vehicle when passing through each of the plurality of intersections based on the captured videos of the plurality of cameras in response to a designation of the retrieval condition including information on time when an incident occurs and feature information on a vehicle causing the incident. The processor superimposes a traveling route of the vehicle on the road map based on the traveling direction extracted for each of the intersections and outputs the traveling route to an output unit.