Well, Jack is a rather shady character, as you can see. He managed to deflect blame on the first day – "you offended me, so I'll stay silent." Convenient if you're a Mafia member. And if you compare it to previous games, when he was a Mafia member or was trying to mislead, it's all very clear. A typical Mafia player. To add to that, yesterday he questioned and asserted, "Are you going to execute Lynx just based on one vote? That's not right," which is part of the set of excuses to avoid being targeted. To add to that, because anyone could say that. But if we assume he's a criminal, it's an additional factor.
Or maybe he decided to slip away under the cover of the commotion, huh?