The only way to see or speak to Moses Ssentamu is through a Plexiglas window at the West Japan Immigration Center in Ibaraki City, so there is no independent way to verify his claims of physical and psychological abuse. But if true, they raise serious concerns about Japan's treatment of visa overstayers and asylum seekers.

Did a group of security guards at the center punch and kick Ssentamu in a coordinated assault in January? Are the authorities at the complex in Osaka Prefecture refusing medical treatment to another inmate, Mujahid Aziz Iqbal, a wheelchair-bound Pakistani? And, most serious of all, do detention centers here deliberately dole out harsh treatment in the hope that detainees will leave the country?

Ssentamu, 35, has been locked up here for over a year since being arrested for overstaying in 2008. Back in his homeland, he says he was active with the opposition Forum for Democratic Change Uganda, and claims to have been arrested and tortured by the authorities. Facing a trial for sedition he knew he couldn't win, he decided to flee the country, leaving behind his wife and four kids.