Upon first meeting him, Jim Moriarty seems normal. He's got a soft voice, and it appears to match his personality until Greg starts questioning him.
"So I couldn't have pleaded insanity, because I'm just as sane as you or anybody else."
"You didn't mean to kill that police officer?"
"No, I couldn't hurt a fly! They know it was an accident. That's not what they're hanging me for. They're hanging me for my beliefs."
"What do you believe in, Jim?" Greg asks, lighting a smoke and taking a drag before offering it to Moriarty.
"Production for use. Oh, I don't smoke."
"Production for use, eh?"
"Yes. Everything has a use, and there's enough for everyone if only we'd use some sense."
Greg takes a minute to take some notes. "Well," he says calmly. "That might just be the answer, Jim."
"It is! It's the only answer."
"Uh huh." There are some roses in the corner of Moriarty's cell, lying next to a picture of a young woman. "Who sent you those roses?"
"Oh," Jim gets a small, shy smile. "Miss Molly Hooper. She's very ni-"
"That her picture there?"
"Yes. She's beautiful, isn't she?"
"She is. We were talking about production for use, Jim. What's a gun for?"
Jim's smile stays in place. "Why, to shoot, of course."
"Do you think that's why you shot that man?"
"I guess. I've never had a gun in my hands before, you know. And production for use has never steered me wrong. I suppose I was confused and thought maybe shooting it would help me make sense of things. That's not crazy is it? Why, that's not crazy at all."
"No, it isn't, Jim."
"You'll tell your readers that, right?"
"Yes I will. Now about Miss Molly, are you thinking on marrying her after all this?"
"Oh no. She's much too good for me."
Just then Anderson sticks his head into the room. "Time's up, Greg."
"Alright." Greg gathers up his things and stands up before moving the chair back to the desk it was sitting at when he came in. "Good luck to you, Jim."
"Thank you, Mr. Lestrade. You won't forget about production for use, will you?"
"Wouldn't dream of it."