MEXICO CITY - Ever since he was exonerated on a murder charge, Jose Antonio Zuniga, 31, stands in front of security cameras and saves receipts, anything to prove where he was at any moment - in hopes of establishing an alibi should he ever find himself in front of a judge again.

“ You don’t trust the police, you don’t feel calm, out on the street,” he said. “There are some things you have lost.”

On December 12, 2005, three policemen grabbed Mr. Zuniga as he was crossing the street in Iztapalapa, at the city’s eastern edge. After two days , he was told that he was being charged with homicide and sent to prison.

“You get to jail and begin to realize that nobody is interested in what you have to say,” Mr. Zuniga said. “Nobody is interested whether you have proof that it wasn’t you. ”

He was sentenced to 20 years in jail based on the testimony of a single 17-year-old eyewitness, a cousin of the victim, Jose Carlos Reyes Pacheco, who was shot to death .

The Mexico City judge in the case - there are no juries in Mexico - convicted Mr. Zuniga despite tests showing that he had never fired a gun. The judge also disqualified the testimony from all the witnesses who said they saw Mr. Zuniga throughout the day of the murder working in his market stall, where he repaired computers .

A film about his case, “Presumed Guilty,” seems like fiction, with unexpected twists, a happy ending and a rap soundtrack composed by Mr. Zuniga and his friends. It lays bare the weak links in Mexico’s effort to build the rule of law . Legal experts hope that the case will give efforts to reform Mexico’s justice structure new energy.

“You can’t combat crime with corrupt police,” said Roberto Hernandez, who made the film with his wife, Layda Negrete.

Mr. Zuniga won a new trial after the filmmakers discovered that his lawyer in the first one had faked his license. But Mr. Zuniga would face the same judge, Hector Palomares .

The filmmakers won permission to film the retrial, while Mr. Zuniga watched from a holding cell.

And it is there that he cracks his own case. He looks squarely at his accuser, Victor Daniel Reyes, repeating his questions until Mr. Reyes admits he never saw Mr. Zuniga kill the victim.

Release seemed a formality. But the judge convicted him again.

Mr. Zuniga recalled thinking : “This trial was worth the trouble. People will be able to see it and ask themselves if this is justice. So the fact that I was sentenced to 20 years again seemed to make sense. Maybe we will be able to change things.”

His luck finally turned after the filmmakers persuaded one of the three appeals magistrates who reviewed the case to look at the trial video. Convinced of “reasonable doubt,” he persuaded his colleagues to release Mr. Zuniga.

For now, he cannot return to his old life, fearful that somebody angry about the film might find him. He only wants to get a high school degree, support his family. “They say that when you design a plan,” he said, “it doesn’t turn out how you expect.”


By ELISABETH MALKIN