[What- bite marks? Oh, uh. What was it about that, again?]

Err, right! Yes! The bite marks were hidden on his finger tip, which is where the blood came from- The blood which he used to write the word "tiara". With that, I made the final connection. You see, the victim must've found out about the stolen crown and mistaken it for a tiara, which was exactly what his dying message alluded to. Mr. Souseki had set his snake upon the victim to silence him, then called it back through the vent with the whistle. He would've gotten away with his crimes too, if it weren't for the Great [meddling] Sherlock Holmes.

And so concludes the tale of the mysterious speckled band!