"I hope for your sakes you were covering your face and hands better than that as you shoveled, citizens," you say, ominously. "These corpses nearest the wall are known to take on the noxious vapors and venoms embedded in the silty soil—not so with the aristocrats entombed in marble. You didn't shatter any bones in your dig, did you?"
"What—what if we did?" says the other graverobber, his deep voice laced with worry.
You shake your head. "Then I hope you held your breath for five minutes afterwards, because the bone-meal particulate, when ingested, brings a lingering death. Have you noted any spotting of the wrists?"
"Enough!" shrieks the lead graverobber, leveling her sword at you. "You're a rascal and a snoop."
"At y'r service," you say with a bow.
"I don't know what you're on about, or why you talk so much—"
"Oh, I was just affording them the chance to position themself," you say casually.
Thwack