 She died of cancer when Debra was 16.Doris is seen briefly in two flashbacks in Season 1, in one seen in a picture that is replicated by the Ice Truck Killer, and in the other urging her husband to contact Dexter's biological father for a blood transfusion, and again in another flashback in Season 2, suggesting that Dexter be tested by a psychologist.Laura Moser is Dexter and Brian's biological mother.