MEXICO CITY, Mexico (Reuters) -- A Mexican court ruled on Tuesday there was insufficient evidence to try former President Luis Echeverria for genocide in a 1971 student massacre, ending a long legal battle to put him behind bars for the bloodshed.

It was a major setback in President Vicente Fox's drive to punish those responsible for state repression during 71 years of single-party rule that ended with his election in 2000.

Echeverria, president from 1970-76, and his former interior minister, Mario Moya, were accused of ordering the attack on student protesters in Mexico City that killed up to 40 people.

But the judge said there was insufficient evidence of genocide. The ruling apparently sinks the case against the 83-year-old Echeverria, which was already reviewed by the Supreme Court on another issue.

Special prosecutor Ignacio Carrillo, appointed by Fox to investigate "dirty war" crimes, said he has no legal recourse to appeal the decision. He said he may present a formal complaint against Judge Herlinda Velasco, whom he branded "a professional exonerator of politicians."

Carrillo still plans to charge Echeverria in a 1968 massacre considered the bloodiest single moment of the crackdown, when he was interior minister.

Survivors of the massacre were crestfallen over Tuesday's ruling. They said it showed an entrenched system of impunity for powerful officials, past and present, still reigns.

"The network of complicity and friendships is still in place," said Jesus Martin del Campo, whose brother was killed in the 1971 attack. "The judge became an accomplice of Echeverria. This is very disappointing."

Genocide test
Echeverria has denied responsibility and his lawyer, Juan Velasquez, said Tuesday's ruling should put to rest the allegations of genocide under his rule.

"In Latin America, Mexico was the only country without a coup, without genocide," Velasquez said of the region's turbulent Cold War years. "Then a government authority compares us to the Nazis. Mexico was not a country of genocide. That's the end of it."

The judge's ruling came as little surprise to international rights groups, who say Echeverria's rule does not compare to the Nazi Holocaust or the mass killings last decade in Rwanda.

"Massive and systematic atrocities were committed including disappearances and executions as well as cases of torture, but there was never any doubt in my mind about the lack of evidence that would support the charge of genocide," said Jose Miguel Vivanco, director of Human Rights Watch Americas.

"This is a very serious setback, but it was foreseeable."

Echeverria was president at the height of a so-called dirty war against leftists, when hundreds of Mexicans died and disappeared at the hands of security forces.

Prosecutors say the 1971 attack was part of a systematic government campaign to eliminate dissidents under Echeverria and other PRI presidents. Victims plan to present a complaint in the 1971 massacre before international rights tribunals.

Last month Mexico's Supreme Court ruled it was not too late to try Echeverria and Moya for genocide, possibly paving the way for genocide charges in other dirty war crimes. It sent the case back to the lower court to decide whether evidence of genocide was sufficient to issue arrest orders.

Copyright 2005 Reuters.