A Twitter war involving film critic Roger Ebert and a great friend of Ryan Dunn erupted as a Pennsylvania coroner investigated the cause of death of the reality television star and daredevil who shot to fame in the Jackass MTV shows and movies.

Dunn and his 30-year-old passenger, Zachary Hartwell, were killed early Monday in a single-vehicle accident in suburban Philadelphia, police said.

The Chester County coroner Tuesday listed blunt force trauma and thermal trauma as the causes of death. Toxicology results will take four to six weeks to complete.

West Goshen Township police declined to discuss the investigation. However, an earlier statement from police suggested speed may have been a factor in the crash.

According to various media, including the Daily Local News website serving Chester County and gossip site TMZ.com, Dunn tweeted a photo of himself drinking with friends hours before the accident.

On Tuesday, TMZ featured pictures of Dunn posing, "glassy-eyed and flushed," in a Philadelphia-area bar called Barnaby's where he and his friends had been in the early hours of Monday before the crash around 2:38 a.m.

Margera 'crying hysterical' after pal's death

Speculation that Dunn had been drinking heavily before the accident prompted Ebert to tweet, "Friends don't let jackasses drink and drive."

Following an intense Twitter and online backlash, Ebert at first defended his tweet by saying the gossip website perezhilton.com agreed with his take on what may have happened with Dunn behind the wheel of his Porsche, saying, "He drank, he drove, 2 people died."

One of Dunn's closest friends, fellow Jackass actor Bam Margera, expressed his fury by angrily tweeting that the film critic should keep his mouth shut.

"I just lost my best friend, I have been crying hysterical for a full day," Margera tweeted, adding that Ebert "has the gall to put in his 2 cents about a jackass drunk driving and [he is] one ... Millions of people are crying right now ...."

Later Tuesday, Ebert blogged on his website that he didn't intend his tweets to be cruel.

"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. I mean that sincerely. It is tragic to lose a loved one."

He added, "I also regret that my tweet about the event was considered cruel. It was not intended as cruel. It was intended as true."

Ebert said he tweeted based on preliminary reports and added, "I have no way of knowing if Ryan Dunn was drunk at the time of his death."

Jackass ran on MTV from 2000 to 2002. Dunn was also in Margera's Viva La Bam from 2003 to 2006, as well as all three Jackass movies.

Dunn's latest reality show was MTV's Homewrecker, billed as "the ultimate in anti-makeover reality shows." He also hosted Proving Ground on the G4 cable network.

In a statement issued Monday, MTV called Dunn "a beloved member of the MTV family for more than a decade."

With files from The Associated Press