See ok, it's a big conspiracy but here is how the whole Khush thing is.
Khush is the mafia Godfather. He devised an elaborate plan with the bomber who has, despite his claims in the dead thread, obviously allied with the the mafia. I don't know how they found each other, but let's not forget that Khush is very cunning and intelligent.
Basically he called on a vote for darkheart, a player no one would soon be leaping to the defence too as he's not the most prominent. Almost immediately, fellow mafia member that guy joins the bandwagon and the trap is set. Soon innocent townies join and their fate is sealed. Khush claims to be the Brother, a claim no one can refute without looking like an opportunist ("nah uh, I'm the brother, protect me!") and draws the protection of the doctor, this in turn sets the Killer off to target another random. With at least 4 people confirmed dead and the high possibility of the killer making 5, the mafia had no need to kill and instead used the time to gather valuable information.
But why take out a fellow mafia member? Obviously the first choice scenario was to have enough townies join that neither mobster would be harmed by the bomber, but earlier that guy let slip that he wouldn't be around for the next few days anyway. Clearly he was expendable. Not to mention being partially responsible for the death of a mafia member makes him appear to be clean. Remember that I tried a similar tactic to success in the January mafia when I led a bandwagon against a teammate and used it as the crux of my defence for the remainder of the game until I ultimately lost in the final day.
We must stop the treacherous Khushrenada now! If not, SOONER. In any case he led to the death of the vigilante and that's unforgivable on it's own.