S5·E17 Double Jeopardy

Are MacLeod and the police seeing a ghost when the evidence in a diamond theft and poison gas murder points to the very evil, but very dead, Xavier St. Cloud? CID Agent Renee Delaney returns to ask for MacLeod's help in finding the killer. Could it be Xavier or simply a memorial to a fallen teacher by Xavier's former student, Morgan D'Estaing?