One reason might be that your son does not carry your name. Was he born out of wedlock? Did you live in the same house as him and teach him to be an honorable man?
Another might be that you never taught your son that it is not right to steal another mans property.
Certainly, it was not right for this store clerk to shoot your son in the back. But your son did provoke the encounter and does have some responsibility for his own death.
Well said Pontiac.