I just took a close look at scene where it appears Harry kills someone holding a handgun. (1:17 in the trailer.) There has been speculation the person in question is Warden Ramirez. It's not him. The person Harry attacks has a full beard and his mustache meets the beard on either side of his chin. Ramirez has a goatee and his mustache does not extend down to his chin. Plus, the clothing of the two individuals doesn't match.
I thought it might be Warden Chandler. The person Harry is blasting appears to be well dressed; something Warden Chandler is known for, and not part of the casually dressed crowd at Mac's. One alternative is that this individual is a Fomor servitor, but, while I don't recall any physical descriptions of the average servitor, I don't picture any of them having beards. Plus, don't they usually wear turtleneck sweaters? So that leads me back to Warden Chandler, but that explanation has another problem. Warden Chandler is described in Peace Talks has having grown a Freddie Mercury mustache, not a full beard. However, the facial hair of the actor in the trailer could be a deliberate mismatch in order to prevent someone, like me, from easily figuring out this mystery.
The lack of a bowler hat does not dissuade me that the individual in question might be Warden Chandler. If Chandler turned out to be a traitor and was forced to take the field against Harry, he might not want any survivors describe seeing a mysterious man in a bowler hat.
Detective Rudolph? Unless he shoots Murphy, I don't think so. Harry would want Rudolph alive to pay the price of being a dirty cop. Killing Rudolph causes nothing but problems and it wouldn't take the heat off of Harry or Murphy.