Who Shanked Teddy? — Gosho Aoyama

Doc Agasa takes Conan and his young Junior Detective League pals to an old, abandoned mansion for a treasure hunt. When the pint-size investigators find a mysterious box, they open it and discover it is full of smashed toys and a violently stabbed teddy bear! Conan follows the trail of clues and runs smack-dab into a dead old man in an attic! Who killed the old man, and more importantly, who killed teddy?