As one of Mexico's most renowned investigative journalists, Manuel Buendia had stepped on a lot of toes by the time he was gunned down in May 1984. But it turns out his murder was more than mere retribution by one of the many corrupt officials and drug runners he had unmasked through his sleuthing.

It now appears Buendia, known by some as Mexico's Jack Anderson, was slain in a sweeping coverup of an international drug-dealing network that had the complicity of the Mexican government and had even looped in the CIA. The intrepid Buendia had tread uncomfortably close to illegal drug operations protected by Mexico's one-time version of the FBI, and used by the CIA to ship arms to contra guerrillas in Nicaragua.

His "Private Network" column had won his country's most prestigious journalism awards. Then-President Miguel de la Madrid attended his funeral. Yet Mexican authorities dragged their feet in investigating his murder. Only last year, the government charged Jose Antonio Zorilla. At the time of the murder, Zorilla was head of the Federal Security Directorate, or DFS, Mexico's FBI. The charges alleged Zorilla plotted the murder for fear the newsman would reveal his ties to the drug trade. Culpability may not end with him. Buendia's investigations into the CIA, trafficking and official corruption gave him enemies in even higher places.

Drug Enforcement Agency documents recently disclosed at a Los Angeles trial in the murder of a DEA agent show Buendia was investigating figures in government and the drug industry. The DEA reports reveal agency interviews with an American, Laurence Victor Harrison, who set up radio communications for Mexican drug barons in the mid-1980s. In an interview last February, Harrison said he knew as an insider that Buendia was investigating links between the drug trade and Mexican officials. Among the officials he was asking questions about was Manuel Bartlett Diaz, then Zorilla's boss as interior minister. Bartlett now is education minister.

Harrison told the DEA that Buendia got some leads from Javier Juarez Vasquez, then-editor of the newspaper Primera Plana. Vasquez's tortured body was found a day after Buendia's murder. Vasquez had told Buendia about a ranch allegedly owned by drug traffickers and used by the CIA to train guerrillas. Apparently Buendia's source also had turned up information about airstrips owned by drug lords and used by the CIA to fly arms to contras. The DEA report says pilots who flew arms were allowed to make the return trip more profitable by picking up cocaine in Colombia. They would refuel at the airstrips en route to Miami.When we asked CIA spokesman Mark Mansfield about the allegations, he insisted the "CIA never used Mexican drug traffickers or territory as a conduit for support of any type to the contras." But contra sources told our associate Dean Boyd that Mexican airstrips had figured into the arms effort. Senate investigators confirmed they were the same ones run by drug traffickers.

Buendia had gotten it all, but what could have been his greatest scoop never made it into print.