In the summer of 1993, not long after a Mexican cardinal was killed at the Guadalajara airport, Father Gerardo Montano was contacted by some old acquaintances. Ramon and Benjamin Arellano Felix, brothers who headed a powerful family drug cartel, had known Father Montano since he was their parish priest in Tijuana in the late 1970s. Now they urged him to send an unusual message to the Roman Catholic pope. Though warrants had been issued for their arrest, the Arellano Felix brothers wanted church leaders to know that they had nothing to do with the murder of Cardinal Juan Posadas Ocampo.

The Posadas murder case is one of the most sensational crimes in recent Mexican history. Official investigations have concluded that the cardinal was a victim of mistaken identity--that hit men for the Arellano Felix brothers confused him with a rival drug lord whom they'd targeted. A new book by Jorge Carpizo, Mexico's attorney general at the time of the killing, and Julian Andrade, supports the official viewpoint. But it contains some new information that opens a window on the complex relationship between church and state. In "Asesinato de un Cardenal," published in April, Carpizo reveals that Montano arranged two meetings between the brothers and Papal Nuncio Girolamo Prigione, then the Vatican's representative in Mexico City. He charges the Catholic priest with being "an accomplice of the Arellano Felix family," and he argues that Montano broke the law by not turning in the brothers when they were wanted by police.

The implication of the accusations reaches beyond the murder mystery. In 1860 Mexico enacted some of the world's strictest laws dividing church and state--and instilled the country with a deep secularism unmatched in most of Latin America. The church, however, largely continued to view itself as self-governing--beholden only to its own laws. It rarely dealt with the justice system. The old attitude was on display this spring when the U.S. pedophile-priest scandal spilled into Mexico. In April the Mexican Conference of Bishops defended the longstanding practice of covering up abuse cases to protect the reputation of the church and the victims. Some clergy members admitted that the church had paid victims "reasonable sums" of money for their silence. "Dirty laundry is best washed at home," Sergio Obespo, a top bishop, told a press conference. The church backed away from that position after a public outcry. "It has taken a long time for the Catholic hierarchy to come to terms with the creation of a higher authority than the church: the state," says Roberto Blancarte, a religion scholar at the Colegio de Mexico.

But it is the slaying of the cardinal that has proved the biggest test of modern church-state relations. Nine years after the event, the government and the church remain at odds over what happened on Monday, May 24, 1993. What's known is that the cardinal's white Grand Marquis arrived at the Guadalajara airport at a very bad time. (He was there to pick up the papal nuncio.) As the prelate stepped out of his car, investigators believe, gunmen mistook him for the enemy drug chief, Joaquin Guzman, or one of his bodyguards, and opened fire. In all, seven people died, none of them drug capos.

Top church officials, including Posadas's successor, Juan Sandoval Iniguez, have never believed the mistaken-identity theory. They've insisted that the cardinal was the target, fueling a popular conspiracy theory that the cardinal must have stumbled upon links between the government and the drug traffickers. Sandoval accuses Carpizo of a cover-up; infuriated, Carpizo once challenged Sandoval to side-by-side lie-detector tests.

It is the 50-year-old Montano--ironically ordained by Posadas--who's become a focal point of the case. He grew up in Tijuana and around 1978 befriended Ruth Corona, who went on to marry Benjamin Arellano Felix. Montano met Benjamin, then in his 20s, in the mid-1980s. In an interview with NEWSWEEK, Montano remembers him as "a well-kept, responsible-looking" man, who said he was a construction contractor. Montano baptized three of Ruth and Benjamin's children. He says that until the 1993 murder case, he had no idea that the Arellano Felix brothers had been pinpointed as drug traffickers. Nearly a decade later, Montano says he still doesn't know if even the drug accusations are true: "I never saw them with arms. I never saw them with drugs."

The priest acknowledges that in November 1993, he arranged a meeting between Ramon and the nuncio. The nuncio went to the residence of President Carlos Salinas in an attempt to persuade him to meet with Ramon, who was waiting back in the nuncio's office with Montano. Heeding the advice of Carpizo, his attorney general, Salinas refused the meeting. In January 1994, Montano arranged a meeting between the nuncio and Benjamin. Montano denies playing any role in a cover-up because he doesn't believe the Arellano Felix brothers were involved in the killing. "My theory is that there was another group contracted exclusively to assassinate the cardinal." He says that Ramon--a man U.S. drug agents claim is responsible for 100 or more murders--was at the airport, but only by chance. Montano adds that another brother, Javier--along with Benjamin--attended a baptism he performed in Tijuana the morning of the killing, and he has the logbook of baptisms to prove it. Prosecutors place both Javier and Ramon Arellano Felix at the Guadalajara airport.

Carpizo asserts that Montano's actions were in part motivated by money. He alleges that Montano falsified the baptism records in exchange for donations to the Tijuana Seminary by the drug cartel. Montano denies that. At the time of the killing, the Arellano Felix organization was becoming the main shipper of Colombian cocaine across the Mexican border into California. The cartel "didn't have the level of national fame they do now," Carpizo says, but "it was known that they were drug traffickers and powerful and advancing in Tijuana."

Failure to turn in a fugitive is against the law in Mexico, but there are exceptions. People considered "close friends" of the suspect are sometimes safe from prosecution. The papal nuncio enjoys the status of ambassador and hence diplomatic immunity. Montano argues that his position as a priest protected him: "In these situations of conscience, we don't have the obligation to go to the authorities."

Prosecutors recently announced that they've reopened the case. The attorney general's office refuses to say whether Montano is being investigated, but he's not been charged with any crimes. Montano, who now heads a modest parish in Ensenada, says the last time he had any contact with the Arellano Felix family was around 1997, when he was stationed in Sacramento, California, and Ruth was living in Chula Vista, near San Diego. Benjamin was finally arrested in March, a month after his brother Ramon was killed by police allegedly working for a rival drug lord.

The election of President Vicente Fox in 2000 raised the hopes of many clergymen that some of the church's old power would be restored. Fox is the first president in more than a century to openly proclaim his faith, attending mass in public and accepting a giant wooden cross from his daughter at his Inauguration. But though he may share the values of the church, Fox has stayed out of its business. If anything, Fox has been moving to make the legal system more independent, which could mean that the church may find itself fighting more battles in court rather than making backdoor arrangements with the powers that be.