There are five conceivable hypotheses"-- here Thorndyke checked them on his fingers as he proceeded--"First, he may still be alive.

Second, he may have died and been buried without identification.

Third, he may have been murdered by some unknown person.
Fourth, he may have been murdered by Hurst and his body concealed.
Fifth, he may have been murdered by his brother.

Let us examine these possibilities seriatim.
"First, he may still be alive.

If he is, he must either have disappeared voluntarily, have lost his memory suddenly and not been identified, or have been imprisoned--on a false charge or otherwise.