I noticed in this movie that after the "Battle of Alcatraz," when he was sent back to Alcatraz with an additional Lifetime Sentence, and though Thompson and Shockley were condemned to the gas chamber, he went through a pretty significant change his attitude. He was just as reserved before their sentencing, but he said that "they went along with people who killed people and that it was all the same." And even though Thompson pointed out that they didn't have any guns and went back to their cells, Carnes said "It doesn't make any difference. We took part." I sometimes wonder if he had a feeling that he was going to be executed, along with Thompson and Shockley, because he felt that he deserved it, just as much as they did. He didn't seem to happy that he was spared the death penalty, unlike Thompson and Shockley. Maybe it was because he knew he'd be in D Block permanently (as far as he knew), but the change in his personality was quite different from the end of the first part of the movie on.
It could be possible that he had a touch of survivor's guilt, but keep in mind that he was a psychopath (just at a young age). I think it just bothered him (even angered him) that he was the only one left to really pay the price that the other three men didn't. Cretzer, Coy, and Hubbard chose their own deaths, as opposed to the gas chamber or what Alcatraz could have done to them for trying to escape (even if they HADN'T killed anybody). Thompson and Shockley were in the same boat as Carnes, but were executed for taking part in the killings and being of age to be executed. Carnes refused to kill anybody and were below the age of execution, and yet he had to go through his punishment alone, so to speak. I think he felt that he was even more the property of Alcatraz than he was before, believing at the time, that he would never be free of that place. When Stroud told him that he was, at least, alive to serve his punishment, he said "Am I?" Growing up in poverty with a Choctaw background, he probably felt that no freedom meant no life. To me, it was a temporary loss of hope on his part, until he helped the three inmates in 1962 escape from the prison.
The Book "Battle at Alcatraz" (instead of the movie) goes into better detail about what happened on May 2, 1946. A good sequel to the book is "Alcatraz Justice." It covers the trial that was subsequent to the three-day-battle. I admit that parts of the trial can be tedious reading, but it is necessary in coverage just the same. I would suggest you first read "Battle at Alcatraz" first, and then follow up with this book.
As far as Carnes is concerned? It's anybody's guess. I do think it was a good point that he was the "only left to really pay the price" and that "he felt that he was even more the property of Alcatraz than he was before." He came to Alcatraz with the reputation of escaping every prison he was ever in. His attempted escape, with the other five inmates, from Alcatraz failed. It was the only prison he didn't actually escape from. He was young, and probably figured Alcatraz was pretty much where he was going to stay for the rest of his life. They put a close watch put on him from 1946 on. It seems to me that Alcatraz never got the best of him because he was able to keep his mind occupied and,ultimately, assisting Frank Morris and the Anglin brothers of their escape, and thus, would have to close Alcatraz.