It is idle speculating about the cause of death in the absence of a doctor.

Death in this case appears to have been due to haemorrhage.

Apparently the murderer aimed at the heart and missed it, and the shot went through the lungs.

The shot was fired at very close range too--look how the wrapper is burnt! Any sign of the bullet, Caldew ?" "I found none." "Well, we shall have to wait for the doctor to clear up these points." His trained eyes swept round the bedroom, taking stock of every article in it.

He next carefully examined the door, and the lock on it.
"The door was open when the others came upstairs, you said, Caldew ?" "Yes--about half open." "That accounts for the scream and the shot being heard so plainly downstairs.