andrea canning (voiceover): time passed, and iliana married, had daughters of her own, but she still thinks about her friend often. do you feel like erika is watching over you? yes, every day. i miss her every day. it's been so many years, and i miss my friend every day. that's all for this edition of "dateline." i'm andrea canning. thank you for watching. [theme music] issue >>> just doesn't make sense. >>> a vibrant young woman stalked by a killer. >> found dead by her boyfriend. >> my brother was just a mess. he was devastated. >> the most ominous clue. >> up on the wall to the left of where heidi's body was, was a number one. >> she is number one, and get ready, because here comes trouble. >> exactly. >> it was not a break-in. the windows, the door, nothing was broken. did the killer have a key? >> the question always was, how did the person get into the house? >> a decade later, in a state 1500 miles away, detectives finally found their answer. >> got a dna hit. >> and more questions. >> we knew there was more to this story than just coming from colorado to commit a murder and g