The unsolved murders of young Karen and Gordon Alexander have haunted Texarkana for more than 40 years.
In April 1981, Karen, 14, and Gordon, 13, were found brutally stabbed to death in their Arkansas-side home.
Infamous serial killer Henry Lee Lucas later claimed to be the murderer, but his confession was found to be false.
The case went cold, but interest has recently increased, in large part because of a Facebook group focused on finding justice for Karen and Gordon.
That new spotlight on the case attracted the attention of this episode's guest.
Texarkana native Cheryl Hester is an expert in the emerging science of forensic genealogy.
Karl and Cheryl talked about what that means and how her skills just might lead to a breakthrough in the Alexander case.