Expensive liquid

Exploration Stage: Secret Room
From: Huntress
Description: I don't know how "The Shadow" and his followers brought paranoid souls into town, but I can't let that happen! Whoa! A hunting crossbow from the weapons rack just fired at me. I dodged it just in time. There was some kind of flask attached to the arrow. Look for it.
Completed: I swear on my sword, it is blood in this magic flask! The second murderer is not just a paranoid nutcase, he tried to perform an alchemical ritual with the blood of his victims! Or something even more horrifying.