midnight
That some person , or persons , must have got admission in this way , appears evident from the fact of the aperture being there . As to the manner in which he -LRB- or they -RRB- obtained access to the roof of the tavern , it is to be remarked that the third house , lower down in the street , was empty , and under repair -- that a long ladder was left by the workmen , leading from the pavement to the top of the house -- and that , on returning to their work , on the morning of the 27th , the men found the plank which they had tied to the ladder , to prevent anyone from using it in their absence , removed , and lying on the ground . As to the possibility of ascending by this ladder , passing over the roofs of the houses , passing back , and descending again , unobserved -- it is discovered , on the evidence of the night policeman , that he only passes through Shore Lane twice in an hour , when out on his beat . The testimony of the inhabitants also declares , that Shore Lane , after midnight , is one of the quietest and loneliest streets in London . Here again , therefore , it seems fair to infer that -- with ordinary caution , and presence of mind -- any man , or men , might have ascended by the ladder , and might have descended again , unobserved . Once on the roof of the tavern , it has been proved , by experiment , that a man might cut through the trap-door , while lying down on it , and that in such a position , the parapet in front of the house would conceal him from the view of anyone passing in the street . Lastly , as to the person , or persons , by whom the crime was committed .