What is interesting is if Christos is Black Council as Harry and Eb both seem to think, why is he going to the Peace Talks instead of being there for the vote?
It's starting to look to me that Cristos is a dupe rather than a player. Harry sees it; even if he doesn't consciously think it, when he suggests to Lara that she use Cristos to broker a deal with Etri. What you've added about Cristos not hanging around at Council HQ to influence the vote against Harry adds to the evidence that Cristos isn't Black Council, but even so, Cristos is someone who might be easily manipulated by a Black Council agent.
And Eb is talking about Harry going off to glad hand and politic for his position, when Harry says he can't because he is on the security team, Eb didn't seem to know about it. Now supposedly he is the head man for the security team, yet it is Carlos who claims to be who wants Harry on the team.. So is it yet another sign of dementia in Eb that he has forgotten that fact? Or is Carlos about to be the one close who stabs Harry in the back? Another thought, the bearded guy Harry blows away in the trailer, Christos?
And yet, according to Carlos it was Ebenezer who sent him to notify Harry about the Peace Talks and that they would take place in Chicago. Eb knew that Carlos had the authority to pick whoever he wanted as part of the security team. He knew that Harry and Carlos had worked closely together in the past, and they had done so on multiple occasions. How could Eb not foresee that Warden Ramirez might want Harry to join the security team, unless as you say, Ebenezer is starting to lose his mental acuity.
The person Harry wastes in the trailer has noticeable facial hair. The people we know who fit that description are Warden Ramirez, Warden Chandler and Detective Rudolph. The description of Senior Council member Cristos doesn't mention any facial hair. The person Harry blasts with the spell has a full beard and mustache which meets the beard. Warden Ramirez (in the trailer) has a goatee but his mustache doesn't reach his beard. Warden Ramirez' clothing doesn't match that of the person Harry is blasting. The clothing that Harry's target is wearing could be something suitable for either Warden Chandler or Detective Rudolph. Harry's target/victim is carrying a handgun. This is suitable for both Rudolph and Chandler. (Chandler's magical ability has to do with the manipulation of time.) Both Warden Chandler and Detective Rudolph are described as having mustaches, but not beards. However, while the mismatch between Warden Ramirez' facial hair and that of the person Harry ices can't be easily explained away; because they both occur in the trailer, the difference between the book description and what we see in the trailer could be a simple misdirection so we don't think it could be either Chandler or Rudolph.
It was Conspiracy Theorist who suggested Detective Rudolph. Initially I didn't like that idea very much, but if Rudolph shot Murphy, then I could see Harry going off on him. I still favor Warden Chandler, but the handgun is more appropriate for Detective Rudolph, so I can't discount him either.