Cain's arrogance in chapter four of Genesis is covering up the guilt for the murder of his brother. Thinking he can fool God he tries to blow Him off with a sarcastic retort about whether or not it is his (Cain's) job to keep track of Able. God calls Cain on it telling him what he has done and cursing him to the life of a nomad.
But this all roots from Cain's rebellious spirit. Earlier in this chapter Cain's sacrifice is rejected because he does not present the Lord with the right offering. The offering here shows that Cain's heart was not in the right place. God calls for obedience to His commands. At this time it was a lamb for an offering symbolizing the coming Christ. Cain gave his first fruits instead. As a result of this rejection Cain became angry with Able because God favored him for obeying Him. Thus, Cain killed Able.
It is interesting to note that although Cain was bothered when he was asked where Able was, there is no sign that he was just as disgruntled when God told Him his sin. Don't we do the same? Can't we be just as hypocritical? We are bothered by the inconvenience of responsibility, but at the same time are taught by the culture that sin is fine and to be expected making it all the more difficult to be in the world, but not of it.