. >> veteran prince george's county homicide detective bernie nelson was in charge of the case. the first arriving officers told him they found the main door locked shut from the inside. the killer, they thought, had likely entered the house through an unlocked side window. >> this bedroom on the second floor that's facing us, that's where carissa was found. >> detective nelson wondered, did the murders have anything to do with the plague of recent home invasion robberies? if so, why was nothing stolen from the house? >> her vehicle was still in the driveway. nothing appeared disturbed. >> investigators didn't find any useful forensic evidence, just six spent shell casings from the bullets that had kill karen and carissa fired from a glock 17 handgun. >> we did find out that just two doors down across the street, someone had seen a blue vehicle parked on the right side of the road and that, right now, at this point, that's all i have. >> reporter: so detective nelson set out to find out more about his victims. karen lofton turned out to be a devoted mother and nurse with no appa