The Democratic presidential candidates will gather on the same stage this afternoon for a debate in Johnston, Iowa. On the eve of that debate, candidate John Edwards rolled through Iowa in a campaign bus with Hollywood actor Tim Robbins as a drawing card for rallies in Iowa City, Grinnell and Des Moines.

"The primary purpose of well-known figures, celebrities is they help attract a crowd and when you attract a crowd, you get to make your case to ’em," Edwards says.

Edwards, who served one term in the U.S. Senate and was a member of the Senate’s Intelligence Committee for four years, says there should be an investigation of the C.I.A.’s decision to destroy two tapes of interrogations of terror suspects. "People need to get to the bottom of this and be held accountable," Edwards says.

That means an independent investigation of the matter, according to Edwards. "I’m completely supportive of an independent prosecutor," Edwards says. "I think that having somebody who is not from the (Bush) administration is the best way to get to the bottom of this." The C.I.A interrogations took place in 2002 and agency officials say they notified congressional leaders in 2003 that they intended to destroy the videotapes. One of the techniques used was waterboarding, which some — like Republican presidential candidate John McCain — label torture.

"The very idea that we’re having a debate about torture in America is offensive in and of itself because America should not tolerate any form of torture and that’s something I intend to do something about as president of the United States," Edwards says, "and the fact that these tapes have been destroyed just feeds the idea that there are things being done that have to be hidden."

Edwards made his comments during an interview with Radio Iowa.

Edwards and the other Democrats campaigning here in Iowa will appear at The Des Moines Register forum this afternoon. It starts at one o’clock and will be broadcast live on Iowa Public Television. IPTV will replay the event at seven o’clock tonight.