“What about the telephone?” Karr asked, his voice gone flat with weariness.
Tragg said, “We have reason to believe that the person who committed that murder had a very definite reason for lifting the telephone receiver.”
Mason avoided Tragg’s eyes.
Karr said, “I suppose he wanted to call someone. You have to lift the receiver to do that, you know.”
“When we first examined that telephone,” Tragg went on, ignoring Karr’s sarcasm, “we noticed only an ordinary desk telephone with two fingerprints which had been outlined in paint on the receiver. Then we made a more detailed investigation and found something which is very peculiar, to say the least.”
Karr said, “Don’t beat around the bush. If you’re trying to accuse me of something, come out and say so.”
Mason said, “He’s just trying to surprise you into an admission of something, Mr. Karr. It’s the way the police work. Apparently a person’s poor health doesn’t change their methods.”
“I’m not accusing you of anything,” Tragg said, ignoring Mason’s interpolation, “but I’m telling you what we found.”
“Well, what did you find?”
“Concealed in the base of that telephone in such a way that it would hardly be noticeable on a superficial examination was a small hole. The telephone was bolted to the desk, which was unusual. We further found that the desk was screwed to the floor so that the telephone and desk were held in one position. That aroused our suspicions. We made a careful examination and found that the base of the telephone contained a very ingenious burglar alarm, a ray of invisible light which could be switched on so that it played across the door of that room. The only way the connection could be broken was by throwing a switch which was on the far side of the light beam, or by picking up the telephone receiver and lifting it from its cradle, which automatically had the effect of cutting off the beam of light.”