וַיֹּ֤אמֶר יְהוָה֙ אֶל־קַ֔יִן אֵ֖י הֶ֣בֶל אָחִ֑יךָ וַיֹּ֙אמֶר֙ לֹ֣א יָדַ֔עְתִּי הֲשֹׁמֵ֥ר אָחִ֖י אָנֹֽכִי׃
And the LORD said unto Cain: ‘Where is Abel thy brother?’ And he said: ‘I know not; am I my brother’s keeper?’
Read kabbalistic (mystical) interpretation of Genesis 4:9: and classical mystical sources.