We all live by assumptions; we must be especially careful about the contexts of scripture. Cain's question, "Am I my brother's keeper?" goes unanswered. Much of the time, the truth does not yield a simple "yes or no" answer. Cain, in his reply to God, was trying (probably in a sarcastic, surly, or smart aleck manner) to deceive or mislead God. A multitude of scriptures reinforce this overarching principle of watching out for our brethren, realizing also that there is a limit to how far we can intercede for someone. Our brethren are not our charges or wards, but our equals.