“Have you traced Brent’s movements the night of the murder?” he demanded.
“Certainly not! But he told us he was out for a stroll at the time, if you remember. He’s hard up and Harrison’s death means a big income to him. Also, Joel showed Brent his treasures a week ago Sunday, including, presumably, the cross-bow. Brent has plenty of motive, no alibi and is a very good shot, Landis. Remember how he hung about that first night when we were questioning Miss Mount? Finally, it’s just possible that Graham knows too much about his financial affairs!”
Landis nodded uncertainly.
“Not much better and no worse than our other theories,” he muttered. “Oh, well, let’s try out the cross-bow, eh?”
They entered Miss Mount’s room and moved quietly through the bathroom into Joel’s den. Five or six minutes later they had wound up the cross-bow, adjusted it to the recent scratches on Miss Mount’s desk, propped up the butt with a book and set the Japanese arrow in the groove of the stock. They sighted along the arrow to find that it pointed straight through the open top of the middle library window and through the reception-room door beyond.
Satisfied on that point, Landis carefully fastened his thread to the trigger, passed it around the knob of the closed bathroom door and holding the thread, dropped the spool out the window into the garden-bed below.
They descended the stairs at the end of the wing, passed out into the grounds, found the spool and carried it to the reception-room window, paying out their thread as they went.
Now Landis, who had carefully tested the pull of the trigger, drew the black thread as taut as he dared and fastened it, with a stout thumbtack, to the lower sash of the window which Miss Mount had closed. The window was open again, the lower sash high above the sill.
“You could simply pull our thread from out here,” he observed to Bernard, “but to prove our theory up to the hilt, the window ought to be actually lowered as Miss Mount lowered it that night.”