MEXICO CITY -- When burglars broke into Mexico's renowned Museum of Anthropology in the predawn hours of Christmas Day 1985 and made off with some of the country's most valuable national treasures, Mexican authorities were shocked and embarrassed. Not only was it one of the biggest museum heists in history, but officials were clueless as to who had done it. Exhaustive checks at ports of exit and border crossings were ordered on the assumption that the pieces would be spirited abroad for sale to foreign collectors. But the massive search turned up nothing, and few Mexicans thought the priceless pre-Columbian artifacts and jewelry -- including the unique jade death mask of an ancient Mayan ruler -- would ever be recovered. So it was that when all but 13 of the 124 purloined pieces were found last month in a private house in a Mexico City suburb, the discovery was hailed as nothing less than miraculous. In fact, the archaeological treasures had been kept in a canvas bag in a bedroom closet for a year after they were stolen and had never left the country. Their recovery came as a fringe benefit of an escalated war on drugs by the government of President Carlos Salinas de Gortari. An investigation by members of a Federal Judicial Police task force resulted in the arrest earlier this year of a suspected drug trafficker who provided authorities with their first break in the mysterious case. Eight suspects eventually were arrested, including one of two former students now charged with the heist. Since the artifacts were found June 9, narcotics investigators have turned up two more sets of ancient relics that evidently had been looted from archaeological sites. In the latest find, investigators raided an abandoned ranch house in the state of Jalisco July 7 after receiving a tip that marijuana was stored there in cardboard boxes. When the police opened the boxes, they found 184 apparently ancient art objects. In a ceremony Thursday to present the recovered items to the Museum of Anthropology, Attorney General Enrique Alvarez del Castillo said that 133 of the pieces -- mostly clay figures and ceramics -- had been identified as authentic relics from western Mexico that were created between 200 B.C. and A.D. 200. Another 21 pieces were being analyzed to determine their authenticity, and the rest were judged to be fakes, he said. Roberto Garcia Moll, director of Mexico's National Institute of Anthropology and History, said the authenticated pieces would be donated to museums in the western states they were believed to have come from. Unfortunately, he said, the fact that the items had been looted from unknown sites had robbed them of some of their value. "What we will never recover are all the elements associated with these objects," Garcia said. "We don't know if they come from tombs, clay floors or some other archaeological sites." By far the most valuable objects, however, were those stolen from the museum in 1985. Their unexpected recovery was cause for national celebration in a country that intensely values its historical past. In a ceremony led by President Salinas and attended by members of his cabinet and scores of invited dignitaries, the artifacts were officially returned to the museum last month for display in a special -- and heavily guarded -- wing of the vast complex on the grounds of Chapultepec Park. Among the recovered objects is the jade death mask of the Mayan ruler Pacal, an Aztec obsidian vase in the form of a monkey, the jade image of a sacred "bat god" from the Zapotec civilization and scores of adornments including intricate gold jewelry and jade necklaces. "We were really lucky that the pieces weren't damaged," said Phil C. Weigand, an archaeological researcher who works in Mexico and Arizona. "There isn't a monetary value for pieces like that." Stealing them, he added, "was like burning the only edition of a volume from the Vatican archives. It was a loss to the heritage of the country." "Each of these objects brings us a message from our past, from ancient civilizations that forged an era of singular glory," said Salinas in presiding over the return of the artifacts. "We have recovered part of our injured pride." Indeed, the theft had forced a humiliated government to admit major flaws in the way the national treasures were guarded. Although museum plans called for a force of 100 security guards, only nine were on duty when the heist occurred, and they were reported to have been "Each of these objects brings us a message from our past, from ancient civilizations that forged an era of singular glory." -- Mexican President Carlos Salinas drunk or sleeping after some on-the-job Christmas Eve celebrating. Officials at the time asserted that the thieves were "experts" and "foreigners," probably from Colombia or Guatemala, but never presented evidence to support that conclusion. In fact, prosecutors now say, the culprits turned out to be two young Mexicans: Carlos Percher Trevino, 28, and Ramon Sardina Garcia, 30, both veterinary students at the time. Percher was arrested last month when the artifacts -- along with some cocaine -- were found in his house in the suburb of Satelite. Sardina remains at large. Among seven others arrested as accomplices of Percher in drug trafficking and covering up the robbery were his brother, Luis, and Isabel Camila Maciero, an Acapulco nightclub star also known as "Princess Yamal." Investigators, citing a confession by Percher, said he and Sardina had planned the heist for six months before carrying it out, visiting the museum some 50 times to case the building, study the displays, take photographs and observe the guards. The investigators gave this version of subsequent events: After celebrating Christmas Eve with their families, the two neighbors changed into black clothing and set out on their mission in Percher's Volkswagen at about 2 a.m. Christmas Day. They crawled into the museum's basement through an air conditioning duct, went through three exhibit rooms and stuffed the most valuable pieces into a canvas bag. They then left the museum the same way they had entered. The whole operation took 30 minutes, and the pair never saw a security guard. Percher then stashed the bag in his bedroom closet, leaving it there for a year while authorities desperately searched for the artifacts and eventually gave up. Percher later moved to Acapulco and befriended drug traffickers there. He traded a couple of the pieces to one of the traffickers for cocaine, and eventually tried to fence the rest of the loot to another drug dealer, Salvador Gutierrez, known as "El Cabo" (the corporal). But when Gutierrez was arrested by narcotics police in the northern border town of Reynosa earlier this year, he fingered Percher. Police kept their quarry under surveillance for 45 days before finally moving in. A few days after his arrest, Percher retracted his confession, asserting it was made under duress. He claimed not to know the other codefendants besides his brother. Since then, according to institute director Garcia, eight more of the 124 stolen pieces have been recovered, leaving only five unaccounted for. The whole affair may have been "a blessing in disguise," said Carolyn Baus, an American curator at the anthropology museum. "People have become more aware of their patrimony and of how valuable these pieces are." As she spoke, a steady stream of Mexicans wound through the new exhibition, peering at the recovered artifacts in their glass cases as guards with automatic rifles stood watch nearby.