Detective Merlin

Merlin the Magician walks down a deserted alleyway when he comes across 4 people kneeling over a dead body. He knows that two of the suspects are knights (and always tell the truth) and two are spies (and always lie). After taking the following statements, Merlin knows which one suspect killed the dead man. Determine the profession (knight or spy) of each suspect, and find the killer.

Suspect A: "Suspect D has the same profession as me."
Suspect B: "Suspect C will say that Suspect A killed the man."
Suspect C: "Suspect A killed the man."
Suspect D: "The dead man was killed by a spy."