User blog comment:Yonkou Rome/Aokiji at Ernies lobby/@comment-1736597-20110818023439

The way I always saw it was he never wanted to catch the crew. He promised he would let Robin go so naturally he let her go. I think Aokiji isn't lazy but more uses that as a excuse to let those who he feel to be innocent go. He recognized that the strawhats were only protecting Robin.