Shaka doesn't know much about the man he shoots at the time—mainly just that the guy had been looking for drugs and got aggressive.
But later Shaka learns more from the victim's godmother. Chris had three children, two daughters and a baby son. Chris had recently lost his own mother to cancer (Afterword.4-12).
Shaka regrets killing almost immediately, but it takes a long time for him to face the full responsibility and forgive himself for it. Shaka writes Chris a letter as one small way to try and express how sorry he is (Prologue.11-23).
He knows it can't restore a lost life, but it helps him honor the person Chris was.