Aaron Paul, Breaking Bad

[WARNING: The following story contains plot details from the Season 3 finale of Breaking Bad. Read at your own risk.]

For much of Breaking Bad's superb third season, Jesse (Aaron Paul) considered himself "the bad guy."

Check out photos of the Breaking Bad cast

He blamed himself for the death of girlfriend Jane (Krysten Ritter), who gave up her sober lifestyle to begin using again with Jesse. But despite that — and Jesse's meth-making efforts with Walt (Bryan Cranston) — Jesse was never a murderer, which Walt realized in this season's penultimate episode, when he killed two rival drug dealers instead of letting Jesse go through with it.

In Sunday's heartbreaking and shocking season finale, however, Jesse finally crossed that line. Realizing their employer Gus (Giancarlo Esposito) would have to keep Walt alive to churn out the amount of meth Gus needed, Walt and Jesse plotted to kill lab assistant Gale (David Costabile), who the duo realized was being groomed to replace Walt.

"The most shocking and dramatic thing we could think of for the end of Season 3 was to take Jesse's character into very much uncharted territory and actually have him murder someone," series creator Vince Gilligan tells TVGuide.com. "Not only to murder someone who is basically an innocent, but to do it for the best of reasons. To be loyal to Walt and keep Walt alive, he does this absolutely despicable, terrible thing. Dramatically, it presents us with potentially limitless opportunity for drama in Season 4."

AMC officially picked up the show for a fourth season late Sunday night.

Breaking Bad finale: All innocence is lost

Although the season-ender wasn't on the same scale of the plane crash in the Season 2 finale, Gilligan notes a commonality: Innocent life is lost because of Walt's actions.

"Walt is the cancer at the center of the show," Gilligan says, highlighting the irony that Walt began making meth to earn money for his family following a terminal cancer diagnosis. "He is a malignant entity on his family and loved ones; [he] harms them and potentially ruins their lives. Walt's bad life choices come back to bear very bitter fruit, not just for him and his own life, but for his friends, family and loved ones. No one escapes the show unscathed."

So, is "good guy" Jesse gone for good?

"I'd love to say I have the whole series plotted out to the end, but I truly don't," Gilligan says. "I think Jesse is indeed the moral center of this criminal equation. I don't know why he couldn't continue to be. If he had lost his soul utterly, he probably wouldn't have a problem that he shot Gale. But I imagine that he's going to have a big problem with it. I'm not sure how it's going to manifest itself. There are many ways, and we're going to examine as many of them as possible."

Breaking Bad's Aaron Paul: Jesse is going to a very dark place

And while Walt seems less and less troubled by the murders he is forced to commit, Gilligan doesn't think we've seen Walt fall as far as he can. "I don't think Walt has completely lost his humanity at all," Gilligan says. "I think if he truly had, there wouldn't be reason to watch the show anymore. He still is a man filled with love for his family, a man who still has all those feelings of guilt and self-loathing for the man he's become and tried very desperately to deny.

"There are still reasons to root for this guy and not give up on him, but I will admit he makes it harder with every episode we show," Gilligan continues. "If the day ever came where he was truly evil and without a soul, that would be the end of our series."

And can Walt escape the series alive?

"I do have a thought," Gilligan says about the series' end game. "It's a very faint, broad-strokes thought for where I'd like to see Walt end up, but if I said what I was thinking, it might ruin it a bit."

What did you think of the Season 3 finale?