The mark was put by Barker's bloodstained slipper upon the windowsill to suggest how the fugitive got away. They obviously were the two who must have heard the sound of the gun; so they gave the alarm exactly as they would have done, but a good half hour after the event.
巴克用他沾了血迹的拖鞋在窗台上做了脚印，伪作凶手逃走的痕迹。他们显然是两个肯定听到枪声的人，所以在他们安排好了以后，才拉铃报警。不过这已经是案发后整整半个小时了。