The Execution of Catherine Willows

A part of Catherine's past comes back to haunt her when a man that she put on death row 15 years ago is about to be executed. However, his execution is postponed a the last moment when new DNA evidence is introduced. Suddenly, a new body turns up at the local college, killed in the same manner of the previous murders, leading to the obvious conclusion that the actual killer may still on the loose... but is it a copycat killer?