C28 Possible Scope of Identity of the Murderer

"Go on!" Elder Liang looked at me curiously.

I said, "Normally, if a bit drills into a human body, the bottom of the hole will create a weak pit because the front end of the bit is pointed. But in these holes, I don't see any holes like that. What kind of drill bit could produce such holes? "

I was puzzled, because I was not a professional in engineering machinery