Keeper

4:9 And the LORD said unto Cain, Where is Abel thy brother? And he said, I know not: Am I my brother's keeper?

I can't tell if God actually doesn't know what happened, or if he's still taunting Cain.

Cain doesn't seem like a good person: he's a murderer and a liar.  It's a wonder God doesn't get along better with him.