A routine shopping trip at one of New York City's busiest department stores turned into a nightmare when a mother changing her baby's nappy was stabbed from behind in a seventh floor bathroom. At the centre of the case is Kerri Aherne, a 43 year old woman from Massachusetts whose past and recent release from psychiatric care have raised urgent questions about public safety, mental health systems and how such a violent attack could unfold in the middle of the holiday rush.
