There was a brief silence, and then, without saying anything, the Sergeant got up from his chair and walked over toward the two pieces of furniture in question. Marsden remained seated, his keen blue eyes fixed thoughtfully upon Colin's face.
"What's your opinion, doctor?" he asked at last.
"I am inclined to agree with Mrs. Ramsay," said Colin. "I think it was the same man who broke into the house before. He is evidently searching for some particular paper or document, and as he couldn't find it in the desk he came back a second time to try and open the safe. On his first visit he probably hadn't got the necessary tools with him."
"And how about the murder?"
Colin hesitated. "There's one thing I don't understand," he frankly admitted. "I left the Professor working in the laboratory, and it's a mystery to me how he managed to reach the study without my hearing him. I was awake the whole time, and I can swear that there wasn't a sound."
"Well, I can explain that to you," said the Inspector. "Mr. Carter didn't cross the hall; he entered the room by the window."
With a sudden exclamation Colin started to his feet.
"By Jove, what an idiot I am!" he exclaimed. "I never thought of that. Of course, there's a side door from the laboratory into the garden."
"I imagined that there must be," said Marsden, "and I haven't the least doubt that we shall find it unlocked." He got up from his chair and glanced at the police surgeon, who was standing by himself in front of the fire. "I don't think we need keep you any longer, Doctor Sinclair," he added. "I'll let you know what time we fix for the P.M. as soon as I've seen Ashford."
The surgeon, who seemed ready enough to depart, picked up his hat and coat.