Fifteen years have passed since human bones were dug up at a construction site in Shinjuku Ward, Tokyo, linked to the infamous wartime Unit 731, and they remain a mystery that authorities still appear reluctant to resolve.

The Group to Investigate the Bones Issue, made up of local residents and scholars, suspects many of the deceased were victims of wartime experiments carried out on prisoners by the notorious Imperial army unit and is calling on the government to use DNA and superimposing technology to examine the remains to verify their origins.

The bones were dug up in July 1989 adjacent to Toyama Park at a site near dozens of low-cost public housing units.