The difference between “a true story” and “inspired by a true story/true events” is laid bare in “Unabomber,” an account of the tail end of the hunt for mad mail bomber Ted Kaczynski.

The heroine, played by Shailene Woodley, is an FBI linguist brought in to analyze the writing style of the man who planted or mailed sixteen bombs, killed three and injured 23 others.

The unknown killer eluded capture for 18 years until the FBI caught a break. But there was no FBI “linguist” named Joanne Miller who parsed the perpetrator’s archaic and sometimes academic writing style, published in screeds culminating in “The Unabomber Manifesto.”

But damn, THAT would have made a fascinating movie and moviegoing thought exercise.

Kaczynyski, a onetime math prodigy and Harvard grad — he was enrolled at 16 — ranted about technology, “industrial society” and academia and sent bombs to airline and university faculty — “UN-A” bomber. He was only caught when his brother recognized the rants as in a style he knew all too well.

Knowing all this doesn’t mean you can’t get a surprising and riveting thriller out of the hunt for a cunning quarry who was every bit as brilliant as the most far-fetched “supervillain,” with a special talent for covering his tracks and living off the grid.

But what Danish director Janus Metz (“Borg vs. McEnroe,” “Armadillo”) and the two credited screenwriters of “Unabomber” serve up is a dull, under-detailed police procedural attached to a sort of “Beautiful Mind” mental breakdown of a madman who wanted to be an important thinker.

Jacob Tremblay of “The Life of Chuck” plays young, late 1950s Chicago-native Ted, son of a working class tyrant of a father who expected great things of him, but an impressionable kid too young to be subjected to CIA backed psychological experiments by a charismatic Harvard professor.

Oscar winner Russell Crowe was an Oscar nominee for his performance in “A Beautiful Mind.” Here, he ably plays a flawed manipulator.

He encourages the kid’s dreams of becoming a philosopher.

“It’s ideas that shape the world!”

But this series of wired-up and studied provocations with an argumentative foe only referred to as “Mr. C.” (Gus Halper) don’t so much sharpen young Ted’s arguments as gut him, psychologically. He learns to be as cruel, ruthless and personal in his vicious expressions of his views of society, “progress,” The Industrial Revolution and the like.

And from that, we infer, a callousness that crosses into mania festers.

Tremblay serves the externals of the character well enough, the meek “submissive” and rules-following Ted who devolves into a killer. But we sense no interior life, and the writings that came to define who this terrorist is aren’t sampled nearly enough to paint a more complete portrait. They’re barely touched on at all.

Crowe’s character is similarly sketched-in, an academic striver working for “The Agency” to see how brain washing works and how to identify those most susceptible to it. The personal conversations between the mentor/tormentor and his “subject” whom he convinces is a “protege” aren’t revealing because we don’t buy them as anything more than other forms of manipulation.

Woodley similarly has too little to play around with, just a fictional character who is always right while her colleagues doggedly go up more and more blind alleys at the direction of a flawed “profile” created by “Langley.”

“He thinks he’s smarter than everyone else,” is her insight. We don’t see or hear enough of the Unabomber’s writing to make that insight with her.

The movie’s revelations are few and far between, as the writings of Kaczynski aren’t used to flesh out what still play as troubling ideas — that a few powerful men are using technology and industrial “progress” to enslave everybody else.

That would be a daring approach for the film to take — that maybe Crazy Ted had a point before crossing this or that line. It’s dangerous point of view to let get around, considering what happened to the creep who ran United Healthcare.

Perhaps that’s why they avoided the rants and ramblings and philosophizing of their subject.

And lacking that dangerous edge, “Unabomber” just passes the time, another F.B.I. procedural with a couple of big names adorning the cast and classing the joint up, with neither their characters nor the screenplay illuminating it or its seriously sinister title character.

Rating: R, violence, profanity

Cast: Shailene Woodley, Jacob Tremblay,Annabelle Wallis, Alexander Ludwig, Matthew Kevin Anderson, Steven Ogg and Russell Crowe.

Credits: Directed by Janus Metz, scripted by Sam Chalesen and Nelson Graves. A Netflix release.

Running time: 1:40