I'm telling you that you got your facts wrong. I didn't kill your brother. But you killed my mother. You might as well have held the gun to her head!
Some things are too terrible to grasp at once. Other things - naked, sputtering, indelible in their horror - are too terrible to really grasp ever at all. It is only later, in solitude, in memory that the realization dawns: when the ashes are cold; when the mourners have departed; when one looks around and finds oneself - quite to one's surprise - in an entirely different world.