I've had a theory about the Doomsday Killer for a couple of episodes now that is starting to feel more likely with each episode. I'll put it in spoiler code, since I'm almost certain I'm right. Don't say I didn't warn you. Spoiler: Dexter I think Travis killed Gellar several years ago, and now the professor exits only in his head, like Dexter's father. I first noticed a couple of episodes ago that their waitress didn't seem to notice him. Then when she was tied up in the kitchen, Gellar stroked her hair, but she kept her eyes on Travis. I've been paying attention ever since, and every time they're out in public, nothing has contradicted that idea. Then in last night's ep, Travis ran into Gellar in the marketplace as soon as Dexter was called away about Brother Sam's shooting. Then Travis's sister tells her students that her brother's a great artist. "Gellar" has been doing those paintings all season, and we even get a lingering shot on one of them this episode. He's a character who doesn't want to give in to his urges, but has this figure in his head driving him to darkness. Flip-side of Dexter.