Strangler

S1, E19: Lucas calls on the ghost of the Boston Strangler to come to Merlyn. Lucas leaves town to attend a convention and Albert De Salva (aka The Boston Strangler) decides to do more than just try to kill Merlyn. He murders a nurse and goes after Gail. Albert tries to gain the trust of Caleb to get to Merlyn. But when Caleb realizes what he is doing, he uses his "special powers" to prevent his sister from being strangled and eliminates Albert.