What exactly is wrong with Karl?

Karl Childers, from Slingblade. He’s referred to as mentally retarded, but he doesn’t seem that way. Maybe a little slow with flawed reasoning skills, but smart enough to be a whiz with small engine repairs, and smart enough to understand the situation with Frank’s family and put together that Doyle will eventually seriously hurt them. So what exactly is his psychological problem?

It’s been a long time since I’ve seen the movie, but could he have been severely autistic? I think that, coupled with being surrounded with people that don’t know how to treat it well and the stigma of being a murderer (he killed his brother, right?) would certainly do a number on someone.

He seems mentally retarded to me - relatively high-functioning, but mentally retarded. Put another way, he may merely have a low IQ.

He has some of the mannerisms that my autistic son has. But I think most of his “damage” was caused by the ignorance of his parents.

His mother and her lover. I don’t think anything was specifically supposed to be “wrong” with him; I think he just wasn’t very bright and had had his entire personality browbeaten out of him in prison. Or maybe became extremely introverted after being secluded for all those years. And I’m sure something snapped inside him when he committed the murders in the first place.