[Salamander]

And we don't know the back-story, either.
The mother may have acted on the final piece of a puzzle to which only she knows the whole answer.

*If* my mom wanted to face it, she could sit and assemble various seemingly unrelated incidents and evidences of physical damage that would reveal the truth to her.
But, she's chosen not to.

[JeffAtlanta]

And we don't know the back-story, either. The mother may have acted on the final piece of a puzzle to which only she knows the whole answer.

If so, that could have been presented to the police and used at trial.

I guess you have no problem is this mother is gunned down by one of the family members of the person she shot do you? The person she shot was someone's son too - she would only be avenging her child who was never even charged with the crime.