Yeah, it's been screamingly obvious since last week who the real Sinnerman was. I mean, no way was the season's big bad going to turn out to be some random guest star. It had to be the recurring character who was connected to the Sinnerman arc. And they practically hung a sign on his back this time, with Chloe observing how unnaturaly stoic Pierce was about the guy who'd allegedly killed his brother. I'm surprised that didn't make her suspicious. She's supposed to be a top detective.
Come to think of it, the name "Pierce" is kind of a clue too, an apt pseudonym for the first murderer -- although the Bible doesn't specify how Cain slew Abel. But I guess "Strangle" or "Bludgeon" wouldn't have worked as well as a surname...
Anyway, if Pierce/Cain is an immortal who's been wandering the Earth as an outcast for thousands of years, I guess that could explain why he's so dull and affectless -- he's seen it all and is deadened to feeling. It doesn't make Tom Welling's performance any more interesting to watch, though. For an immortal, he's amazingly lifeless.
Hold on -- Cain. As in Dean Cain, the last person to play Clark Kent in live action before Welling did. Don't tell me they cast this guy in the role because of a Superman in-joke.