Was actor Bob Crane a likable, All-American guy? Or was he a depraved sex pervert?

The answer is he was a bit of both.

But the further question of what motivated him to become that way is one of the many things left unanswered in the Crane biopic “Auto Focus.” Considering the topic, performances and production skill that went into the picture, it should be a knockout. But the movie is a curiously detached, sometimes hollow account of the TV star. Although it entertainingly details his adult life, it ultimately reveals very little.

Greg Kinnear (“As Good As It Gets”) portrays Crane, a Los Angeles DJ who catches his big break in 1965 when cast as the lead in the World War II POW sitcom “Hogan’s Heroes.” (As one character describes, “It’s the show with the ‘funny’ Nazis.”) A non-drinking, happily married man with three kids, Crane seems to have everything going his way.

When the star runs into a gear-head named John Carpenter (Willem Dafoe), the man introduces him to the dawning age of video equipment.

“I can wire anything,” Carpenter boasts.

Soon Crane is wired to his own libido.

As the cheerier mid-’60s give rise to the sleazier early ’70s, the pair becomes increasingly drawn into a cycle of swinging sexual conquests. The generically handsome actor has the physical skill to lure the girls, and the cloying Carpenter has the technological skill to record the encounters.

Willem Dafoe, left, and Greg Kinnear star in Auto

The volatile combination results in tragedy.

Paul Schrader, the writer of films such as “Taxi Driver” and “Hardcore,” is no stranger to the topic of men being sucked into seedy environments they have difficulty escaping. Although functioning solely as director on “Auto Focus” (the screenplay was written by newcomer Michael Gerbosi, and adapted from “The Murder of Bob Crane” by novelist Robert Graysmith), Schrader’s characteristic themes of carnal obsession resonate throughout the story.

Yet the director gets so heavy-handed with his delivery that the movie nearly becomes a parody at points. It starts out lovingly creating the bright hues and brimming optimism of California in 1964. (Kinnear is first seen hosting a peppy morning radio show that subtly hints at the naughty nature of his character.)

As Crane is gradually drawn into the world of sex, lies and videotape, the film’s vivid technicolors give way to a grainy, desaturated look. The static cameras go to wobbly hand-held shots. The suave big-band jazz is replaced by ominous synthesizers. Kinnear might as well be wearing a T-shirt that says “doomed” to go along with his aviator glasses and 3-day-stubble.

Schrader’s near-documentary approach in the second half is also perforated by a ridiculous fantasy sequence that takes place on the set of “Hogan’s Heroes” during its final season in 1971. Here, Crane’s workplace and sexual cravings are combined into a silly, vulgar orgy involving his castmates and family. The gimmick is completely out of place in relation to the rest of film, which is composed in such a straightforward manner.

Not all of the later scenes succumb to these flaws, however. Some of the best occur during conversations between Crane and his stoic manager Lenny (Ron Leibman). Even as the washed-up actor is being tendered for unlikely roles such as in Disney’s “Superdad,” his manager understands the depths of Crane’s descent. Lenny advises him to evaluate the “conflict between your lifestyle and your career.”

That counsel is never heeded.

Crane was found beaten to death in 1978 while staying at a Scottsdale, Ariz., hotel room. The murder weapon was thought to be a camera tripod, and a video cable was tied around his neck. The crime remains unsolved. Although police suspected Carpenter and the movie implies his guilt he was never convicted. (Carpenter’s death in the 1990s only adds to the mystery.)

While “Auto Focus” is in many ways a standard downer biopic, Kinnear’s performance is anything but by-the-numbers. He’s spot-on in the recreations of “Hogan’s Heroes” episodes, manifesting Crane’s smug, comfortable demeanor and bland charm. And he convincingly changes from good guy to lecher with the same ease. (Like Crane, Kinnear’s career path took him from hipster radio to fluff television to movies.)

Witness a scene in which he attempts to pick up women at a nightclub. He instructs the bartender to set the TV to a station he knows is broadcasting reruns of his hit comedy. When a woman recognizes him sitting next to his image on TV, he takes full advantage. Kinnear’s calculated reaction of false modesty is priceless.

If this superficial gambit was in any way a reflection of Bob Crane’s real personality, it speaks volumes about the man. But the film merely hints at the factors that led to the actor’s downfall. Even with Kinnear’s best efforts, “Auto Focus” is a blurry portrait.