Sherlock Holmes - Deductions

“Judging by its effect upon my brother, I should think it must be a most extraordinary one.” He snuggled down in his armchair. “Now, Watson, let us have the facts.”
“Government employ. Behold the link with Brother Mycroft!”

“There we have it at last, Watson! British government — Woolwich. Arsenal — technical papers — Brother Mycroft, the chain is complete.”

“Then we must take that as our working hypothesis. Young West took the papers. Now this could only be done by having a false key —”
“Several false keys. He had to open the building and the room.”
“He had, then, several false keys. He took the papers to London to sell the secret, intending, no doubt, to have the plans themselves back in the safe next morning before they were missed. While in London on this treasonable mission he met his end.”

“But consider the facts. Is it a coincidence that it is found at the very point where the train pitches and sways as it comes round on the points? Is not that the place where an object upon the roof might be expected to fall off? The points would affect no object inside the train. Either the body fell from the roof, or a very curious coincidence has occurred. But now consider the question of the blood. Of course, there was no bleeding on the line if the body had bled elsewhere. Each fact is suggestive in itself. Together they have a cumulative force.”
“And the ticket, too!” I cried.
“Exactly. We could not explain the absence of a ticket. This would explain it. Everything fits together.”

"Now it must be evident to you, Watson, that this young man’s body was placed on the roof of the train. That was clear from the instant that I determined the fact that it was from the roof, and not from a carriage, that he had fallen.”
“Could it not have been dropped from a bridge?”
“I should say it was impossible. If you examine the roofs you will find that they are slightly rounded, and there is no railing round them. Therefore, we can say for certain that young Cadogan West was placed on it.”

His little fan of yellow light shone upon a low window.
“Here we are, Watson — this must be the one.” He threw it open, and as he did so there was a low, harsh murmur, growing steadily into a loud roar as a train dashed past us in the darkness. Holmes swept his light along the window-sill. It was thickly coated with soot from the passing engines, but the black surface was blurred and rubbed in places.
“You can see where they rested the body. Halloa, Watson! what is this? There can be no doubt that it is a blood mark.” He was pointing to faint discolourations along the woodwork of the window. “Here it is on the stone of the stair also. The demonstration is complete."

“I can assure you,” said Holmes, “that every essential is already known. We know that you were pressed for money; that you took an impress of the keys which your brother held; and that you entered into a correspondence with Oberstein, who answered your letters through the advertisement columns of the Daily Telegraph. We are aware that you went down to the office in the fog on Monday night, but that you were seen and followed by young Cadogan West, who had probably some previous reason to suspect you. He saw your theft, but could not give the alarm, as it was just possible that you were taking the papers to your brother in London. Leaving all his private concerns, like the good citizen that he was, he followed you closely in the fog and kept at your heels until you reached this very house. There he intervened, and then it was, Colonel Walter, that to treason you added the more terrible crime of murder.”