These quotes are a bit out of order, but they're from a similar point in time, just as a disclaimer:
I want to highlight that Luka had Prof and GAD in his POE, also want to put a bigger emphasis on GAD here.
Luka can't find a better reason than OMGUS to vote Prof;
When confronted about the vote, and how he can justify placing Prof together with Poyser (in this case specifically), he had this to say:
I don't like how he's been softing Gram.
And when you bring this interaction between Luka and Gram into perspective with the previous highlighted posts, it looks extremely suspicious;
Luka was really hard flip flopping on GAD last phase, according to himself GAD was in PoE - the main one at that - but he wouldn't really discuss or entertain the topic much outside of that offhand interaction with Gram.
And then when you take into consideration that GAD's role would kill the last voter, Luka's timing and positioning on the wagon is also quite convenient - on top of his final comment that if GAD was town he'd tunnel Prof.. of all people?
I was clearly one of the greatest pushers of GAD, yet he singles out Prof?
TBH, the last mafia might actually just be Luka