We're assuming a lot of things here.
The first assumption that is being made (at least by akro) is that there's 3 mafia members total. 2 mafia is standard in a 9 man game, and this game had 18. We need to look out for 3 more mafia.
Another assumption is that Chris is sane, and I think that everybody should always at least have the thought in the back of their mind that he isn't. Don't rely every decision you make based on Chris's sanity.
That said, I feel like we can test his sanity relatively easy and not at the cost of any night actions. Rust's statements don't sit well with me at all. Is his role really that valuable that he will not even claim the person, while 17 other member's roles are aware? (or at least claimed)
Let's compare rust with animask. Both were disinterested in this game, however animask, with little to care about, claimed his role when prodded to do so. It didn't require any thinking, everybody else was doing it, and he planned on dropping out anyway, thus he claimed.
Rust also expresses disinterest, and wishes to be replaced (also note: animask requested modkill, rust requested replacement). The only difference is, he is not giving any information on his role. Is his role really that game breaking? Is there already not many powerhouse roles in this game that mafia can choose between when nighttime comes? If his role is that important, why does he not have any information for us by day 3?
I'm more certain now than ever that Chris is either insane/naive, and rust is mafia.
I believe a modkill is standard play when a player expresses disinterest, and no replacements are available? Perhaps faceman doesn't wish to do so, because it will be quite the game-changer (and his mafia teammates won't be too satisfied with him)
Also, just to clarify, rust is the only member of Chris's D2 results that has not yet be (nearly)confirmed. If we do lynch him, and he is mafia, this opens up the door for Chris tonight to give town more valuable information tomorrow.
With all of that said, vote: rust
