Mafia 11. X-men

It's version number 1.
The killer is Tieru, i.e., Sabertooth.
The clue for the first night: "calmness" - i.e., an opposition.

The clue for the second night: "heart" - it's simpler here. Firstly, there's a direct reference to the heart on the U-bar, and secondly, in general, sworn enemies are struck in the heart. There are many different statements about this.

Added 4 minutes later

He ripped out the heart; it was clearly Sabertooth who did it, just like on the first night.
And let's see what I found about you today.
Your U-bar: Windrunner.
We enter this into the search and end up here: http://wow.gameguru.ru/wotlk/heroes/...indrunner.html
or here: http://wow.blizzard-rus.ru/worldwarcraft/view/2071/

And now we read what the killer of Ara said - something about conquering the world. He said: "You are pathetic, little humans! You will all submit to us, the mutants!" Now, let's replace "mutants" with "undead"... and it becomes very similar to the link I gave above.

So, I'm voting to execute Zubr!

The phrase is a clear reference to the mafia, that's one thing. Secondly, Windrunner is a good character from Dota.
Although, since you're so blatantly trying to frame me, it's worth thinking about this phrase; there might be an additional clue there...
Hmm, you, the mafia, are trying to get rid of me at any cost: if not at night, then during the day.