Note: if mind emulation is a process which destroys the biological mind (quite probable), then these robots are the end result of an *execution* process, rather than the middling stage of an incarceration process.
My bet: the (presumed) prisoners have nothing directly to do with the robots which now house versions of their minds. Imprinting blank hardware with mind copies is just the quick and dirty way this (apparently post-apocalyptic) city programs new robots. The Japanese Robots purchase this batch, then "free" them by wiping all implanted software restrictions (that's what the sudden blanking of all their chest plates means). The new robots are then in theory free to go anywhere *except* back inside the city . . . but with nowhere else to go, they usually "choose" to follow the Japanese Robots and join their society.