Let's start with the clues. As always, there's a huge mess here. Except for one unnatural turn of events that seemed unusual to me.
The click of the weapon being taken off safety sounded like a bell toll.
Furthermore, I'd like to note that the murder of Gumer was most likely committed by Winterson. The pistol only fits her, and it would also be logical for the mafia to have her do the killing.
And then there's the unclear attempt by the maniac to kill Arandor...