So far, Mr. López Obrador’s supporters have made up the bulk of the people going to the film. For many of them it has only confirmed what they felt in their gut last year.

“I always have thought there was fraud,” said Sandra Quiñones, a 36-year-old city employee, who saw the film in Mexico City. “I would have thought that as a documentary it was boring. But, no, on the contrary, the truth is you come out angry, the great anger of knowing they stole the presidency.”

Others with different political leanings remain in quiet thought long after the film has ended. “I voted for Calderón,” said Araceli Pliego, 23, a student, as she left a Mexico City theater. “At the time, I liked his proposal and I still say he’s not bad as a governor, but after seeing the film, I have a lot of doubts about what happened last year.”

The film does not present new evidence of fraud. But it does assemble for the first time a chronology of all the factors leading to Mr. López Obrador’s defeat. It also shows how election officials rigidly interpreted the law to prevent a wider recount.

The spine of the film is a long interview with Mr. López Obrador in which he contends that an oligarchy of business leaders that has ruled Mexico for generations did everything possible to keep him out of office. He also admitted, for the first time, that he had misjudged the power of the negative advertising against him. Mr. Calderón declined to be interviewed by the filmmakers.

The film also presents images suggesting dirty tricks. At some polling places, ballot boxes were apparently opened illegally; at others, more ballots were apparently cast than there were voters on the lists.

The film falls short, however, of demonstrating that the problems were extensive enough to nullify the results. The courts found the irregularities cut both ways and were not numerous enough to change the outcome.