What made Aaron Hernandez kill — and kill himself?

Millions of people have pondered the question. Now the world’s most accomplished mystery writer has tried to answer it.

James Patterson’s “All-American Murder: The Rise and Fall of Aaron Hernandez, the Superstar Whose Life Ended on Murderers’ Row” came out Monday, just after Hernandez’s old team made another Super Bowl.

That’s good timing by Patterson, whose craftsmanship and marketing have sold more than 300 million books. Most of them were fictional mysteries, and you can see why he’d be drawn to this real-life crime drama.

There’s no doubt Hernandez killed one man and probably two more.

The mystery is why.

How does a guy with a dream NFL life become a homicidal maniac and ultimately hang himself in his jail cell?

Was it childhood emotional trauma? Too much coddling at Florida? Concussions that left him with the worst case of CTE that researchers had ever seen?

Or was Hernandez just plain evil?

Patterson dives into the psychological puzzle, but let me save you the $35 list price. The book doesn’t live up to the hype.

It’s billed as “the definitive, never before told account” of Hernandez’s epic fall. It’s definitive in the sense that nobody had written a 320-page book about it.

The problem is those pages are basically a compilation of previously reported facts, incidents and transcripts. Patterson and his co-writers conducted more than 70 interviews but found no fresh insight into Hernandez’s twisted mind.

If you’d never heard of the case you might like the book as much as Patterson’s best-sellers. In those, the author could just make up a satisfying ending.

Real life isn’t so tidy, but I still expected some payoff along the way.

Like, did Hernandez really shoot a guy when he was at Florida? How many drug tests did he actually fail, and to what extent were his misdeeds covered up?

That’s spawned countless debates around Florida since Hernandez left for the NFL in 2010.

“To his credit, Urban Meyer did his best to mentor Hernandez, making himself available to Aaron day and night,” Patterson wrote.

We knew about the Bible study and Meyer’s Father Flanagan approach. We also know what the culture was around Gainesville.

“We could do whatever we wanted to,” an unidentified player said. “Everyone knew us. We were celebrities. We ran the city.”

There is a juicy book to be written about that era in Gators history, but it will require an author with deeper knowledge of the material.

Patterson is probably the first person to ever describe Meyer as “the rangy, plainspoken coach.” And the book states that in 2007, Florida set “the NCAA record for most players arrested in the course of a single year.”

The NCAA keeps a lot of records, but “most arrests” is not one of them.

Patriots and Court TV fans won’t learn much new about the post-UF Hernandez.

He liked to party. He got mixed up with bad influences from his Connecticut hometown.

He could be charming, combative, charitable and paranoid.

Was he a gang member or bisexual?

The book addresses those issues but sheds no new light on them. Then there’s the unanswered question whether Hernandez committed suicide so that his conviction, which was being appealed, would have to be nullified.

The book painstakingly details how on April 19, 2017, Hernandez stripped naked, wrote “John 3:16” in his own blood on his cell wall, poured shampoo the floor to make it slippery and hanged himself with a twisted bedsheet.

“By the time the guards found him,” Patterson wrote, “Aaron Hernandez was cold to the touch.”

We knew that’s how the story ended.

We’re still not close to understanding why.