For seven years Hailey Sisco and her brother, Dustin, have been haunted by the brutal killing of their father Mike Sisco, and his fiancée, Karen Harkness. Even more troubling for the siblings is that no arrests have ever been made and the case remains unsolved. But Hailey believes she knows who was responsible and is determined to prove the unthinkable. Karen and Mike were both divorced with kids of their own when they met, but the couple was undoubtedly a perfect match. They had been dating for about four years when, in July of 2002, they were gunned down while in bed at Karen's Topeka, Kan., home. Both suffered multiple gunshot wounds but no one heard a thing. While Mike and Karen were well-liked and respected with seemingly no enemies, police believed it was a carefully planned murder - one that left them with no concrete clues. There was no forced entry, nothing stolen, and no signs of a struggle. Ever since, Hailey has been relentless in her quest to prove what she believes to be the heartbreaking truth and bring her father's killer to justice. Now, "48 Hours Mystery" brings in private investigators, Paul Ciolino, of Chicago, and Joe Moura, of Boston, to examine the case and the bizarre twist to the murders that some people claim, was there all along. Correspondent Harold Dow reports.