Suppose that this man Boone had thrust Neville St.Clair through the window, there is no human eye which could have seen the deed.
What would he do then?
It would of course instantly strike him that he must get rid of the tell-tale garments.

He would seize the coat, then, and be in the act of throwing it out, when it would occur to him that it would swim and not sink.

He has little time, for he has heard the scuffle downstairs when the wife tried to force her way up, and perhaps he has already heard from his Lascar confederate that the police are hurrying up the street.
There is not an instant to be lost.

He rushes to some secret hoard, where he has accumulated the fruits of his beggary, and he stuffs all the coins upon which he can lay his hands into the pockets to make sure of the coat's sinking.

He throws it out, and would have done the same with the other garments had not he heard the rush of steps below, and only just had time to close the window when the police appeared." "It certainly sounds feasible." "Well, we will take it as a working hypothesis for want of a better.