Prosecuting geriatrics for what they may have done a lifetime ago seems to me to be a severe disservice to society.
Still, going after small fries after so many years leaves me with a bad aftertaste. I know they're the only ones still alive, but they were also among the least responsible.
It's true guards were mostly volunteers, but genocide wasn't exactly in the job description and young men of 18 can be easily manipulated, moreso under a totalitarian regime.