Read it through once

At the very instant when he brought the loop over his head previous to slipping it beneath his arm-pits, and when the old gentleman before-mentioned (who had clung so tight to the railing of the bridge as to resist the force of the crowd, and retain his position) earnestly warned those about him that the man was about to lower himself down--at that very instant the murderer, looking behind him on the roof, threw his arms above his head, and uttered a yell of terror.