Japanese police today began questioning a junior high schoolboy suspected of murdering a four-year-old boy who was apparently thrown from a 20-metre-high carpark roof.

Japan's NHK TV reported that police had obtained a security video that captured the image of a young man with Shun Tanemoto, who was kidnapped and killed near a shopping mall in Japan's south-western Nagasaki prefecture.

They believe that the local junior high school student was involved in the murder.