In the exhaustive and at times exhausting new biography “Untouchable: The Strange Life and Tragic Death of Michael Jackson,” journalist Randall Sullivan presents a radical new theory concerning one of the most heavily scrutinized public figures of the last half-century. Namely, that the man revered worldwide as the King of Pop could not possibly have been a child molester.

The book posits that Jackson resisted sex for all his days and died in 2009 a 50-year-old virgin.

To support that difficult-to-prove claim, Sullivan takes a two-pronged approach. He attempts to paint Jackson’s $15-million out-of-court settlement with Jordan Chandler (the 12-year-old who accused the performer of having sexually molested him in 1993) as a textbook extortion case. The payout, Sullivan writes, was the “worst decision” Jackson ever made.

Second, the author lays out the almost Dickensian misery of the singer’s early life: performing in dingy strip clubs at age 8, hitting puberty while surrounded by frenzied groupies who terrified him and once even being locked by his brothers in a hotel room with two adult prostitutes (with whom Jackson forswore sexual contact).

Moreover, Joseph Jackson is described as the performer’s “vain, domineering brute” of a father, who effectively robbed Michael of a childhood by forcing him into the spotlight so young and physically beating performance perfectionism into him.

It all combined to engender the superstar’s peculiar penchant for surrounding himself with children, one of Jackson’s few respites from the crushing demands of fame. That controversial lifestyle choice, “Untouchable” contends, ended up costing him everything.

“It was understood that Michael Jackson sought the company of prepubescent males because he yearned to be one himself,” Sullivan writes. “(He) wasn’t trying to be heterosexual or homosexual or even asexual, but rather presexual.”

The 704-page tome – which has already sparked outrage among Jackson’s fans for a prosthetic-nose-and-all depiction of its subject – arrives as the most comprehensive effort to chronicle the mess of his last five years on Earth. It was a period of harrowing personal tumult, heavy chemical dependency and financial implosion, during which the singer came perilously close to winding up in prison.

Longtime Rolling Stone magazine contributor Sullivan does an effective job of humanizing and providing a psychological rationale for much of the King of Pop’s most bizarre behavior. But “Untouchable” buckles under the weight of its reportage.

It’s overlong and feels overstuffed with extraneous detail, especially in the book’s final fourth, which takes up the story after the singer’s death, serving to question the validity of his will, chronicle the battle for control of Jackson’s estate and examine the murky medical circumstances surrounding his death — all while establishing the Jackson clan as the worst kind of scheming money grubbers.

The author struggles valiantly to untie the Gordian Knot of Jackson’s myriad legal entanglements and higgledy-piggledy, megabuck business dealings.

Jackson made a bad habit of reneging on handshake deals for seven-figure loans and then entering into competing business agreements, egged on by greedy family members or various individuals who would represent themselves as his “manager,” with or without Jackson’s consent. These arrangements almost invariably went sour and mired the superstar in legal entanglements.

“Michael went through life knowing that anybody he developed a relationship with was eventually going to sue him,” Jackson criminal defense attorney Tom Mesereau says in the book. “And yet he kept hoping it would turn out differently each time.”

Sullivan’s forensic accounting also extends to the pop superstar’s wildly profligate spending habits — how his seven-figure shopping sprees for antiques, jewelry and luxury cars helped Jackson achieve a sedative-like calm.

Never mind how that kind of conspicuous consumption also wound up putting the Peter Pan of pop $567 million in debt, even at a time when he was reaping a staggering yearly fortune from his business investments and continuing music sales.

Sullivan gives a vivid rendering of the star’s years in exile, “a kind of Flying Dutchman wandering the globe,” after being acquitted in his 2005 criminal trial.

He first exploited the generosity of Sheik Abdullah bin Hamad bin Isa Al Khalifa, second son of Bahrain’s king, to the tune of $7 million.

And later, when Jackson grew disenchanted with life in the Middle East, he castle-hopped in Ireland with his children in tow, trying to kick-start his creative process with the help of a who’s who of Top 40 pop stars.

But by its final six chapters – up to date through relatively recent Jackson family mini-scandals, including Prince Michael “Blanket” Jackson being allegedly menaced with a Taser by a cousin and the odd case of matriarch Katherine Jackson’s supposed “kidnapping” to Arizona – “Untouchable” morphs from a penetrating expose into a joyless slog.

Even while the book’s scope and depth are certainly its key selling points, the mind-numbing catalog of Jackson’s legal labyrinth, roll call of interfamily beefs and humongous cast of shady characters makes for a strenuous read.

With its 53-page afterward and 189 pages of sourcing, “Untouchable” ultimately functions more like a document of record than literature.