Still, Darby decided he had to turn in the pictures but he didn't want his friends to know that he had done it.
Asked why it was important to him to remain anonymous, Darby says, "I knew a lot of them wouldn't understand and would view me being a stool pigeon or however, a rat, however you want to put it."
"You knew there would be some kind of investigation?" Cooper asks.
"I knew these people were going to prison," Darby says. And in his opinion, they deserved to go to prison.
Darby copied Graner's pictures onto a disc and put it in an envelope with an anonymous letter. He took the envelope to the Criminal Investigations Division -- CID -- and told them it had been left on his desk.
"I said, 'This was left in my office. I was told to give it to the CID.' I said, 'Have a nice day, Sir,' and turned around and walked away," Darby recalls.
Darby hoped that would be the end of it but within less than 45 minutes, the investigator came to him.
And the investigator knew that Darby wasn't telling the truth. He promised to keep Darby's name secret, and convinced him to explain how he had really gotten those pictures. Then investigators immediately began to round up the suspects.
"Once they were brought in, once this investigation began, were they removed from the base?" Cooper asks.
"No," Darby says. "They still had their weapons. They still had unlimited access to the facility and me the whole time, for almost a month."
He says he was very scared and even slept with a pistol under his pillow. "With my hand on it. I put it in my pillow case, I put my hand on it and cocked it, cocked the hammer and I'd sleep with it under my hand under my pillow," he remembers.
He slept like this every night. "I slept in a room by myself. And anybody could come in in the middle of the night. You walk in the door, you hang a left, and then come in and cut my throat," Darby says.
"And you really thought that could happen, someone could cut your throat?" Cooper asks.
"I knew that if they found out who did it, they would be after me," he says.
Weeks later, the guards under investigation were removed and Darby could finally sleep without a gun under his pillow. The suspects were gone, and his name was still secret.
Several months later, 60 Minutes II broke the story of the pictures. An article in "The New Yorker" revealed Darby's role, though no one in Iraq seemed to notice.
But then, while Darby was having lunch in the mess hall watching Donald Rumsfeld testify before Congress about Abu Ghraib, the defense secretary said, "There are many who did their duty professionally and we should mention that as well. First, Specialist Joseph Darby, who alerted appropriate authorities that abuses were occurring."
"I just stopped in mid bite. I was eating and I just stopped. What the hell just happened? Now the anxiety came back. Now, I'm worried," Darby remembers. "Everyone in the unit knew within four hours."
What was the reaction?
"It wasn't as bad as I thought it would be. You know, I got support," Darby says.