Master has posed another riddle and I could use some help solving it. As we were wandering through the graveyard one midnight dreary, we noticed that someone had dug up the coffin of a wicked old witch named Eviline.

A group of four frightful fiends were standing around the open gravea vampire, a werewolf, a zombie and a mummy.

"Who has unearthed this wicked witch?" Doctor Arcana demanded an answer.

The vampire said "It wasn't me!"
The werewolf said "It was the zombie!"
The zombie said "It was the vampire!"
The mummy said "No it wasn't!"

Doctor Arcana said "I know that only one of you is telling the truth, therefor, I have deduced the true guilty party."

"Master," I asked, "who dug her up, and how did you know?"
"Thrall," he said, "I will let you solve this mystery for yourself."

I can't figure this out and my brain is starting to hurt. Can anyone help me?

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