New Aaron Hernandez book tries to answer the unanswerable: Why?

"This isn't a whodunit," Patterson said. "It's a why-dunit."

The new nonfiction book -- titled "All-American Murder: The Rise and Fall of Aaron Hernandez, the Superstar Whose Life Ended on Murderers' Row" -- tracks Hernandez's remarkable fall from grace, from star New England Patriots tight end to suicidal prisoner. "All-American Murder" is written by Patterson and Alex Abramovich with Mike Harvkey.

In many ways, the story writes itself. Once a star player who signed a $40 million contract in 2012, Hernandez was convicted of the 2013 murder of Odin Lloyd and sentenced to life in prison. He was also charged with but acquitted of killing two men at a Boston bar in 2012, and was accused of shooting his former friend Alexander Bradley months later.

He ultimately hanged himself in prison less than a week after that acquittal. He was 27.

Patterson has his own theories of why Hernandez's life fell apart: drugs, psychopathic tendencies and football-related chronic traumatic encephalopathy (CTE).

"I think there's a lot of evidence that he was pretty confused, that he had a lot of anger management problems and they kept getting worse," Patterson said.

CNN spoke to the acclaimed author about Hernandez's life and death, his drug problem and why the NFL's head injury problem isn't going away. The interview below has been edited for length and clarity.

Q: Why did you choose this story?

A lot of pieces. One, when I was a teenager, my family moved up outside of Boston, so I watched the Patriots and the Celtics and the Red Sox, so that's (part of the reason), when you're connected to the team a little. I'm not a crazy football fan, but I watch.

Secondly, for me, this is kind of the most dramatic of high profile murder stories, maybe in 20 years or so. Including OJ (Simpson). OJ was an incident. It was one horrifying night. I think if it had happened in Buffalo, where he played his pro ball, it would have faded away a lot faster. But because it happened in LA, and Hollywood, and the Dream Team was assembled, it took on a life of its own beyond the one bad night.

This (Hernandez) thing ... this isn't a whodunit, it's a whydunit. It's an unbelievable fall from grace that Aaron Hernandez took.

He was a very handsome man, he had this amazing smile and dimple when he wanted to use it. He could charm people. He had a $40 million contract. A beautiful fiancee, who had been his high school sweetheart. Baby girl. Unbelievable football talent both in college at the University of Florida and in the pros.

And it all went up in smoke.

Q: Do you mean that literally, as in drugs?

For me, my own theories, I think there were definitely some psychopathic tendencies with this guy. They started early. He, at least theoretically, shot at least four people.

Secondly, the CTE was serious. They got the results from Boston University hospital while I was writing the book. They uncovered that he had worse damage than they'd seen in anybody under 45 years old. So it was pretty severe.

And then drugs -- PCP, coke, a lot of weed, and a pretty steady diet of it. So I think a combination of all those things is what really did him in.

He was tremendously confused by the end. The murder of Odin Lloyd -- who was another friend of his, and going out with Hernandez's fiancee's sister -- he did it a mile from his house, which is crazy. Who in their right mind would do that?

He left four shells by the body, which is crazy. I mean, doesn't he ever watch TV? Pick up the shells. He left a cell phone in Odin's pocket with several calls to him. He left the car keys in Odin's pocket. That was the car that he had rented for Odin with his name on it.

When the police came and they saw the name Aaron Hernandez on the keys, they didn't think it was him. They thought it had to be some other Aaron Hernandez. He shot out a sign on his way out of the lot. He left a shell in the car he was in.

It seemed to me he was gone, he was gonzo that night. And once again a combination of, apparently, he liked to or didn't mind shooting people. That's strange. The CTE, presumably, I mean he was getting more and more paranoid. And then I guess that there were some drugs involved that night.

Q: How much did you know this before, and what did you learn in reporting the book and writing the book?

We got a lot of help from the police in Connecticut and in North Attleboro and in Florida. So I think we got a lot of new stuff from them. A lot of the athletes in Gainesville were kind of ... the University seemed to do a pretty good job of protecting the athletes. But we got a lot from the police.

The NFL (gave me) nothing, and the Patriots nothing. ... I can understand why they might not want to get involved because there are a lot of lawsuits flying around now. And the CTE thing, obviously they don't want more publicity brought to that. But you know what? It's gonna happen and they're gonna have to keep dealing with it.

Q: What stood out from your interviews with police and others you interviewed? What stood out the most?

I think how impressive Hernandez could be at times, and what a knucklehead he was at other times. He really could impress people and charm people.

I think (Patriots owner) Robert Kraft on some level was charmed by him. I think (former University of Florida head coach) Urban Meyer was. And a lot of people tried to help him.

Urban Meyer -- look, you send your kid off to college, and to some extent I mean the kid's got to kind of watch out for themselves. Urban Meyer would have this guy in for Bible study three or four times a week. He had him over the house a lot. He asked Tim Tebow to room with Hernandez on the road. So I think he did a pretty good job and I think he became a bit of a father figure.

(Bristol County) Sheriff (Thomas) Hodgson, at the first jail that Aaron was in, I think he was a father figure.

Clearly one of the big incidents for Aaron was that his father was this kind of big hero in Bristol. He had played for University of Connecticut. He was kind of beloved. When Aaron was 16, (his) father went in for a hernia operation and died.

His father really looked over and watched over Aaron and his brother, and I don't know if it would have totally made a difference, but I think his father would have kept him away from some of the people he started associating with in Bristol.

Q: Did you get any closer to figuring out why he committed suicide?

Once again, and I think you saw it in the last year or so, I think he was just getting more and more troubled, more confused, more paranoid. Like in Boston, when somebody spills a drink on him and he's taking it to new paranoid heights. So I think there's a lot of evidence that he was pretty confused, that he had a lot of anger management problems and they kept getting worse.

One piece of the theory is that in his confused state, he honestly believed that if you believed in Jesus you would get saved.

So that he would be -- I think that may have been something to do with the putting the quote on his forehead. ... That may be a piece of it, and also he knew at that point, he knew about the law in Massachusetts that if he died while the case was being adjudicated that he would be declared not guilty. And he felt that his fiancee would -- and he said to her on the last phone call, he said you're gonna be rich. Or you are rich.