“Slipped under my door here when I opened it this morning. You know Mr. Dolan does not open my office save on Saturdays, when he cleans. Whoever put the paper under the door chose a time when no one was likely to see him.”
“You threw this in the basket as soon as you read it, sir?”
“Yes, for, as I remarked, I was indignant,” replied the professor, curiously wondering what all these questions implied.
“And at that early time I don’t suppose you were using your ink at all, sir?”
“Certainly not, Frank. What makes you ask that, lad?”
Frank spread the paper, which he had smoothed out, before the gentleman.
“You see, sir, whoever wrote this used ink; and in some way or other he must have gotten a certain small amount on his fingers and thumb. Look here, and you will see where there is a very plain imprint of a thumb, and from the other marks that accompany it, I should say that it is the left thumb, too!”
“You interest me amazingly, my boy. And it is all just as you say. I do declare, it must be the left thumb that has left an imprint here. I see what you have in mind, Frank. Go your own way about it. If you discover the guilty one, I leave it to you entirely whether you bring him before me or not. This is your especial affair, and you can manage it as you please.”
“Well, I happened to be reading lately how they take the imprint of criminals’ thumbs over in France, and that no two are exactly alike. With other measurements, it is called the Bertillon system, and has been found to work well. There, I have made an impression of my left thumb, and you can see, sir, that the lines are very much unlike this one.”
“Frank, you are correct, and I give you credit for so much acumen. But do you want me to call every boy in school in here and take an impression of each left thumb, so that we can discover the one rascal?” smiled the principal.