What sort of person is the murderer?
A man physically like either David or Robert, so like that 'Rabbit Jack' would swear to the identity of either of them as readily as to the person of the real murderer.

Why did he use such a weird instrument as the Ko-Katana?
Because he found it under his hand and recognised its sinister purpose, to be left implanted in the breast or brain of an enemy's lifeless body.
Where is the man now?
In London, perhaps outside this building, perhaps watching the Northumberland Avenue Hotel, waiting quietly for another chance to take the life of the person who caused us to reopen this inquiry.

To sum up, Winter, let us find such an individual, a Hume-Frazer with black, deadly eyes, with a cold, calculating, remorseless brain, with a knowledge of trick and fence not generally an attribute of the Anglo-Saxon race--let us lay hands on him, I say, and you can book him for kingdom come, _via_ the Old Bailey." "Yes, sir!" broke in Winter excitedly.

"But the motive!" "Et tu, Brute! Would the disciple rend his master?
Have I not told you that Capella will bring that knowledge with him from Naples?
I have hopes even of your long-nosed friend, Holden, giving us all the details we need." "What did the murderer steal from Sir Alan's writing-desk, from the drawer broken open before the blow was struck ?" Smith entered, bearing a chicken.
"The motive, Winter! The motive!" laughed Brett, and in pursuance of his invariable practice, he refused to say another word about the crime or its perpetrator during the meal..