“This is a tragedy for two families,” Mr. Smith added. “I just don’t think my son was ready to come back in regular society.”

Mr. Smith thinks that his son’s mind became poisoned by war, and Dwight Jr. seems to think that as well. I couldn’t get access to him in prison, but in a recent handwritten letter to his father (which is posted with the online version of this column), he wrote:

“I am going to be honest with you dad. I have killed a lot of men and children. Some that didn’t even do anything for me to kill them. Also some that begged for mercy. I have a problem. I think I got addicted to killing people. I could kill someone go to sleep wake up and forget that it ever happened. It got normal for me to be that way. I never wanted to be this way. I just took my job way to serious. I took things to the extreme. Anyone can tell you that I changed. It is like being a completely different person.”

If Sergeant Smith did indeed randomly kill civilians in Iraq or Afghanistan, I could find no record of that. What is clearer is that he was exposed to concussions while in combat, apparently at least two of them. One occurred when he was in Iraq and his Humvee was thrown into the air in an explosion. He was not visibly injured.

Then, in March 2011, a mortar shell landed near him in Afghanistan and blew him 15 feet in the air, shattering a ceramic plate in his body armor, according to his public defender, Bradley V. Manning. Sergeant Smith was hospitalized, flown back to the United States, and given a diagnosis of a traumatic brain injury with post-traumatic stress disorder.

Jasmin Smith, a 29-year-old German woman who is now his wife, and was then his girlfriend, recalls seeing him in the hospital shortly after his return.

“He was in a wheelchair,” she said. “His hand was shaking. He looked pretty bad. He didn’t say anything for 15 or 20 minutes. At the beginning, he didn’t even recognize me.”