Why all three? There could easily be a patron, a courtesan, and a couple of non-player characters sitting there. So, if Amka isn't lying, we could try to frame Ment.
Why specifically Ment, and what does Amko have to do with it?
There is. The fact that the possessed person was howling and clutching his throat is not evidence, but a reminder of this characteristic.
But I think Arandor gave the artifact to the Enchanter. Or not?

Барон "Vampires"
Отдай свои прошлые сны,
В сомненьях себя обрети,
В бешеном танце душа кружится!
Не думай, что будет потом,
Здесь и сейчас мы живем,
Стань хоть на миг сам собой, слышишь!