The X-Files, Season 8

Doggett:
We, uh, we caught this killer, Jeb Dukes. He's in the ICU - He may not make it.

Mulder:
And now you're wondering if there really was a connection? (Doggett gives him a slight look) ..You know, when I uh, I first came to work at the FBI, I worked at Violent Crimes. And I saw.. I saw the worst of humanity - I saw monsters. And I wondered how they became that way, how these men became so evil. I knew there were psychological explanations - victims of their environment, victims of their parents - but.. the scientific explanations were never truly satisfying, and I began to think about evil like a disease. You know it goes from man to man or age to age. Most of us walk around thinking we're incapable of any acts of evil, and we are - You know we can stifle that momentary urge to kill, or to hurt. We have some kind of immunity to it. But I think it's possible that there's.. an occurrence in somebody's life; a tragedy or a loss that.. leaves them vulnerable - hurts their immunity to evil. And all of a sudden, at that point in their lives, when they're weakened - they're open to evil, and they can become evil.

Doggett:
If that were true, then what you're saying is.. this man when wheeled in here tonight is infected with evil - The same evil that killed my son.. You really believe that, Agent Mulder?

Mulder:
Uh, I'm not really a good test for questions like that - I'll believe almost anything, you know? But the uh.. the pisser is that you may never know. It may be like Agent Reyes says, it could be random and meaningless - who it affects, who it goes to.

Doggett:
What if it isn't?

Mulder:
Well then you'd be seeing something I don't, Agent Doggett.