Kujaku no Dance, Dare ga Mita?

A former police officer was killed on Christmas Eve in the snow. A suspect was taken into custody, and the case was considered resolved. However, a letter discovered after the officer's death and addressed to his daughter casts doubt on the arrest. In the letter, the officer listed names and stated that if anyone on the list was detained or charged, they were not guilty. The person currently in custody for the murder was among those named.