This is a couple of years old, but it's still an engrossing read.
Susan Klebold, mother of one of the Columbine killers, tells about finding out that her son had just passed into American legend as one of our most horrible murderers.
You get the feeling there's a lot of backstory that we don't know, but you do feel sorry for her, like she was clueless in many ways.
"We Need to Talk About Kevin," by Lionel Shriver, tackles a Columbine-like massacre from the perspective of the shooter's mother. It's a good read.