That's what Monsieur de Marquet thinks.

He has had it sent to the municipal laboratory at Paris to be analysed.

In fact, he thinks he has detected on it, not only the blood of the last victim, but other stains of dried blood, evidences of previous crimes." "A mutton-bone in the hand of a skilled assassin is a frightful weapon," said Rouletabille, "a more certain weapon than a heavy hammer." "The scoundrel has proved it to be so," said Monsieur Robert Darzac, sadly.

"The joint of the bone found exactly fits the wound inflicted.
"My belief is that the wound would have been mortal, if the murderer's blow had not been arrested in the act by Mademoiselle Stangerson's revolver.

Wounded in the hand, he dropped the mutton-bone and fled.
Unfortunately, the blow had been already given, and Mademoiselle was stunned after having been nearly strangled.