Mercurio's the "man on the couch" who got shot and needed "medicine"
he sells you weapons if you don't rat him out to LaCroix
and you need only talk to Vandal a couple of times in the clinic to figure out he's Therese/Jeanette's ghoul
if you managed to hack into Therese's computer, you'd also get confirmation!
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Black Turtle
all you need