For two mothers who lost their daughters, amidst the grief persist painful questions.

A week after Maria Pesantez and Mellie Carballo died, apparently from a lethal overdose of heroin and cocaine in a Lower East Side apartment, the families of the girls continue to agonize over how such a tragedy could have occurred.

Both were 18 and college students. Neither had a history of using drugs, said their relatives.

Over the past week, both families have struggled to reconcile the images they have of their daughters with the still-sketchy details of their final hours.

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