So there have been a lot of theories about why Locke is after chief. And why Arby is with him etc, and I had a little thought:
So imagine for a second that Locke has been tasked with the assassination of Halsey and not chief. Where would he start? Chief gas gone AWOL (most likely to find Halsey) and will probably be a hell of a lot easier to track down than Jul and Halsey.
So Locke goes to the arbiter, offering a partnership. Arby wants Jul gone, and Halsey is with him, Locke tells him that if they can track and follow chief they will find both Halsey and Jul. (chief always gets his mission done no matter what)
Arbiter said something in a previous trailer along the lines of “how well do you know your friend Spartan, and what will you call me when you learn the truth of what I have done” So, perhaps the Arbiter os aware of cortanas death, he knows chief needs Halsey to (bring her back? Look for help?) and yet, for the sake of his race, Arby agrees to help Locke track down and kill Halsey, even though it could be chiefs last hope of saving Cortana.
343 did say this would be the darkest halo, other than losing Cortana, feeling betrayed by the arbiter and losing your last thread of hope is pretty dark if you ask me.
and i know there’s the bullet trailer showing the sniper rifle bullet shattering chiefs helmet but hey, its all speculation at the moment right! They may just be throwing us off…
SPECULATE!