Some crimes are easy to solve, but many detectives are haunted by the one they couldn't close.
The 1980 murder of 19-year-old Sandra Cassidy Williams was one such case, going unsolved for 39 years.
Now, a Mobile Police Department cold case detective believes they've got their man, arresting 61-year-old Alvin Ray Allen.
The crime happened so long ago that Allen would have been 22 at the time of Sandra's murder. Allen is now charged with murder and is out of jail on a $100,000 bond.
Solving a murder this old has it's own set of problems.
NBC 15's Darwin Singleton spoke with the actual detective on the case.