Anonymous wrote:My mother's stepfather was a member of the KKK. Hard to think of something worse than that. I believe my mother. If you trust your mother to tell you the truth, ask her.
I think OP's grandfather was KKK -- or something similar -- too. I'm guessing the "bad thing" was being present at/participating in a lynching? That fits the idea that he was "guilty by association."
OP, ask yourself what you hope to gain by asking your mother about this. Isee only three possible outcomes:
1. It just upsets her.
2. She tries to deny it, which you won't believe.
3. She tries to justify it, which (as you said) would affect your feelings about her.
I'm not sure there is an upside at this point. Given her age, I think you may have missed your opportunity.
However, I can see your desire to know more, and perhaps to 'right the wrong.' Was this crime solved in its time? I'm guessing your grandfather wasn't punished for it, but were others? Did the victim of the crime get any justice? If not, I think you could pursue it through other channels -- Google, local newspaper archives, Ancestry.com, maybe? - to try and cleanse the family name or at least find out what your grandfather's role really was and whether there is anything you could do at this point to improve the karmic balance.