Sentence 4 questions the enduring appeal of specific crimes and the reason for their repeated examination.
Sentence 1 elaborates on this inquiry, identifying "unusual elements" that engage a specific audience, thereby refining the scope.
Sentence 2 suggests contributing factors to the appeal of these cases, such as extreme depravity or mysterious circumstances.
Sentence 3 then expands the scope, proposing that unresolved cases, which may resist resolution, possess an appeal distinct from "ordinary" murder cases, emphasizing the persistent fascination with unsolved mysteries in criminal contexts.
Therefore, the correct option is (A): 4123