>> the investigation begins with some tough questions for kion. coming up. >> would you have hurt your mom and sister? >> one of the detectives blatantly said everybody in that room thinks it's you. >> was it? what happened next would launch a whole new wave of fear when "dateline" continues. with soothing honey-licious taste. nyquil honey. the nighttime, sniffling, sneezing, coughing, aching, stuffy head, fever best sleep with a cold medicine. i can'twhat? ve it. that our new house is haunted by casper the friendly ghost? hey jill! hey kurt! movies? i'll get snacks! no, i can't believe how easy it was to save hundreds of dollars on our car insurance with geico. i got snacks! ohhh, i got popcorn, i got caramel corn, i got kettle corn. am i chewing too loud? believe it! geico could save you fifteen percent or more on car insurance. >> reporter: a mother and her daughter, executed. detective bernie nelson had investigated hundreds of murders. had learned to keep the recurring images of death at arm's length. but this case was different, he was a fat