Over lunch, Henley recalled, Andrea Neiers pressed the filmmakers to examine phone records and police reports she claimed would prove her daughter's innocence. "I had the misfortune of sitting between Alexis and her mom, and there was constant cross-talking," Henley said on set of the movie in Venice Beach last year. "I think they're flattered. And seemingly crazy."

"They were helpful," Coppola added. "But the most helpful has really been Brett Goodkin."

Goodkin served as the lead detective in the case and was a paid consultant on the movie. For $12,500, Coppola said he advised on the realities of arresting a suspect and in a surprise turn agreed to play himself in one scene — slapping the cuffs on Watson's character.

Goodkin, however, soon became the subject of an internal affairs probe into whether he failed to get permission from the LAPD to work on the movie, and whether he neglected to inform the district attorney about his role. At the time of production last year, Ames, Tamayo and Lopez were awaiting trial — and eventually were offered probation in plea deals.

"You should all write a thank-you letter to Goodkin, because his judgment is as poor as it gets," Judge Larry P. Fidler said while addressing their attorneys last July. "You can have a field day with his credibility during trial.... It's a shame what he did. It's harmful to the people's case."

Goodkin, who refused requests for comment, is awaiting a ruling from a disciplinary panel.

Another player in the real-life crimes — burglary victim Paris Hilton — also got involved with the film. She allowed Coppola to shoot in her mansion, which moviegoers will see is adorned with a stripper pole, a shoe rack organized by designer and numerous framed photos of herself.

Hilton attended the Cannes premiere and told a reporter that she felt violated watching the scenes in which the criminals ransack her house. "During some parts of it, I literally had tears in my eyes and I wanted to cry," she told New York Magazine's Vulture blog. "It just made me really angry and upset, and when I see these kids, I want to, like, slap them."

Watson, whose pole dancing and other bad behavior in "Bling Ring" seems a concerted effort to move beyond her goody-two-shoes "Harry Potter" role, agrees the characters can be hard to watch.

My character "is everything that I felt really strongly against — she's superficial, materialistic, vain, amoral," Watson, 23, told British GQ in May. " I realized that I really hated her. How do you play someone that you hate?"

But even Watson found herself being sucked into the allure of celebrity while filming with Hilton and being around her excess.

"She said goodbye to me and said 'nice to meet you, gorgeous,'" Watson recalled. "And I was like, 'whoa, my life just got really weird."

amy.kaufman@latimes.com

Steve Zeitchik in Cannes, France, contributed to this report.