Kennedy picked up the tube containing the solution made from the towel spots. "This antivenin was your product, doctor?"
"Probably so," was the precise answer.
"Then the purchasers can be identified," I suggested.
"We have no record of ordinary purchasers," Nagoya explained, slowly.
Kennedy was keenly disappointed at that, and showed it. However, he thanked the scientist cordially, and we departed. Outside, he turned to me.
"Do you understand now why the night intruder at Tarrytown did not die—if he is one of our suspects—from the scratch of the needle?"
"You mean he had taken an injection of antivenin before—"
"Exactly! We are dealing with a criminal of diabolical cleverness. Not only did he make all his plans to kill Miss Lamar with the greatest possible care, but he prepared against accident to himself. He was taking no chances. He inoculated himself with a protective serum. The needle of the syringe he used for that purpose he wiped upon the towel you discovered in the washroom."