I remember someone in the Bible asking God this question also.... Genesis 4:9 Then the LORD said to Cain, "Where is your brother Abel?"
"I don't know," he replied. "Am I my brother's keeper?"
6 Then the LORD said to Cain, "Why are you angry? Why is your face downcast? 7 If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must master it."