First of all, I should make this clear that this is inspired by a movie I've just watched (Gone Baby Gone) not by any real life incident.
Basically, the story for anyone who hasn't seen it is a 3 yr old girl is abducted. Her aunt hires some private investigators to augment the police investigation. The mother is a lowlife; alcoholic, drug using, drug running, leaving the kid alone all the time or taking her to bars. She isn't too bothered by the abduction, figuring that it's in retaliation for $130,000 she stole from a drug dealer while acting as a mule. Anyway, seems the child is killed (drowned). Family mourns. Story goes on.
Near the end, the investigator finds out that the child's uncle & members of the police were in on the abduction. The death was staged & the child is now living very happily with the retired head of the child abduction unit (police). The dilemna is: let the kid go on living with people who love & care for her & can provide for her, or destroy the police chief & his wife and give the kid back to the mother.
Of course, he does the latter, and the mother goes back to her drinking and not caring for the kid. Only, it's worse, because the little girl now has no uncle & aunt to breach the gap in care.
My view was leave her where she was, though I understand that's ethically & legally wrong.
I'd be interested to see what anyone else thinks.