Last Seen is a search tool for the first few minutes after someone goes missing inside a building. A member of staff describes the person out loud, and Last Seen searches every camera, shows the people who fit, and asks a quick question when two of them look alike, so the right person gets picked instead of guessed. From there it follows them across cameras on a 3D model of the building. When they walk somewhere no camera covers, it shows how far they could have got, clears the areas the cameras can see are empty, and ranks the cameras and rooms worth checking first, until a camera picks them up again and confirms it is the same person. We built it on NVIDIA’s synthetic hospital footage and used only half of the cameras, keeping the rest hidden so we could check our guesses against where people really were. The footage runs through the VAST DataEngine pipeline into VastDB, which holds the video search index, our tracks and our person index. NVIDIA Cosmos Reason describes each person and checks what it says against two camera views, Cosmos Embed matches descriptions to people, YOLO11 finds people in each frame, and Canary turns speech into the search. Weights & Biases serverless inference runs the agent’s reasoning, Weave traces and scores every step, CoreWeave GPUs serve the models, and we built the whole thing in Cursor.