Right. Locked room, one bullet, no prosecutions. Lets say it's a Webley .455- enough to guarantee the kill, but it's not gonna stretch to two of 'em if ones stood behind the other..... shame. Who gets it?
Without wishing to offend FP or Auxie, logic suggests that this challenge demands the following approach.
1. You conceal the Webley about your person.
2. You, Blair, Frenchperson and Auxie will all detest Newton Dunn. Therefore, the three of gang up to kill him. Blair will inevitably be wearing that 'lucky tie' of his, borrow that and while FP, Blair and Auxie hold him down, you use the tie to asyphixiate Newton Dunn.
3. While Blair is composing the usual (in)sincere tribute he makes when someone in the public eye (no matter how vaguely) meets their demise, and is thus not concentrating properly, the three arrsers gang up on the former PM and kill him with his own neckwear in the same fashion that Newton Dunn met his maker. Ensure you retain control of the tie.
4. On the basis that time spent on recce & info gathering is seldom wasted, discover an area where Auxie and FP violently disagree. Having identified said area, fan the flames so that Auxie and FP come to blows. Stay out of the fight, bar offering salient points to inflame their anger towards one another. At some point, one of them will fall to the floor. If they both end up on the floor, identify which is in the less advantageous position.
Leap into the fray and either strangle your identified victim with Blair's tie, or bash his head into the floor until expiration occurs.
5. With the two of you left, use the Webley as a club to inflict fatal head injuries on the other arrser.
6. Use the .455 round to blow the lock off the door Hollywood-stylee