"Lawrence found out what flight they were putting you on," she said. "He's not entirely bad, at the end of the day. We couldn't let you go back alone, Bee. Could we Batman?" (11.112)
Ultimately, Lawrence, whatever his motivation, contributes to the possibility of justice for Little Bee. But since it means being separated from Sarah, it seems like a decent-sized sacrifice. Still, we don't get to know Lawrence well enough to get a good sense of what exactly motivates him.