More likely he is suffering from adult onset schizophrenia.

I'm not saying that there's no such thing, but it shouldn't be blamed for everything.

I've known WWI vets who were very damaged: "Shell shock." Known one who survived gas as well.

I've known WWII vets, ditto. One shirttail relative lost most of his fellow unit members in Indonesia and was still having nightmares sixty years later. Another was a colonel who turned over German POWs to the Free French, only to hear the latter mass execute them moments later, just out of sight. Discussing it brought tears to his eyes, sixty years later. 

Santiago should have been medicated. Talk therapy isn't going to fix a biological problem.