Ryan Dunn, left and Zachary Hartwell, right. The man in the middle is unidentified. Ryan Dunn, left and Zachary Hartwell, right. The man in the middle is unidentified.

Bam Margera slammed Roger Ebert on Twitter after the film critic tweeted: "Friends don't let jackasses drink and drive."

Meantime, police have identified Ryan Dunn's passenger as Zachary Hartwell, a production assistant on Jackass.  Both men died when Dunn's Porsche jumped a guardrail in West Goshen Township, Pa., crashed into a tree and burst into flames.

Hartwell was credited as a production assistant on Jackass: Number Two and as a stunt driver in Minghags, a 2009 film co-directed by Dunn's friend and Jackass star, Margera.

Jackass star Ryan Dunn killed in car crash

Hartwell appeared drinking with Dunn in a photo (pictured: Hartwell is on the right) that Dunn posted on his Tumblr hours before the Monday morning crash — which led to Ebert's tweet, and Margera's emotional response."I just lost my best friend, I have been crying hysterical for a full day," Margera wrote

, "and piece of s--- Roger Ebert has the gall to put in his 2 cents about a jackass drunk driving and his is one, f--- you! Millions of people are crying right now, shut your fat f---ing mouth!Police have yet to determine whether alcohol was involved in the crash, only stating that "speed may have been a contributing factor."

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Ebert blogged Tuesday that his tweet wasn't meant to be insensitive. "To begin with, I offer my sympathy to Ryan Dunn's family and friends, and to those of Zachary Hartwell, who also died in the crash," he wrote. "I mean that sincerely. It is tragic to lose a loved one. I also regret that my tweet about the event was considered cruel. It was not intended as cruel. It was intended as true. I have no way of knowing if Ryan Dunn was drunk at the time of his death. ... What did I mean by that? I meant exactly what I wrote. I wasn't calling Ryan Dunn a jackass. In Twitter shorthand, I was referring to his association with Jackass."Meanwhile, G4 has pulled Dunn's new stunt show, Proving Ground, in which he recreated professional stunts from film, TV and video games in real life. The eight-episode series premiered last week. A network rep said discussions are under way about the show's future.