Beaten with a shovel, a drill bit in his head, and clubbed to death

Question: A man named Tom goes to a party. Him and three guests go into a back room to play some games. A few hours later the four of them are discovered dead. One was beaten with a shovel, another had a drill bit in his head, and the other had been clubbed to death. Tom has no marks on his body.

How did he die?

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