Masked gunmen on Tuesday shot and killed a prominent Tijuana journalist who was investigating the 1988 shooting death of one of the founders of his newspaper.

Francisco Ortiz Franco was shot four times in his car just before noon on a busy street in downtown Tijuana, the rough border city south of San Diego. A release from his newspaper, Zeta, said he was shot while leaving a physical therapy session accompanied by his sons, ages 10 and 8.

Ortiz, 48, was an editor and one of the founders at the weekly newspaper best known for its investigative reporting about government corruption and drug trafficking. He was the third Zeta journalist ambushed and shot in 16 years. Co-founder Hector Felix Miranda was shot and killed in 1988; Jesus Blancornelas, co-founder and publisher, was severely wounded and his bodyguard was killed in an attack in 1997.

Blancornelas still runs the newspaper and is guarded around the clock by a large group of soldiers and police officers. One of his attackers, who was killed by a ricocheting bullet, was identified as an assassin from the Arellano Felix drug cartel whose picture had recently appeared on Zeta's front page.

The Felix Miranda case remains a major political issue in Tijuana. Two men were convicted in the shooting and sentenced to prison. They were both security guards at a racetrack owned by Jorge Hank Rhon, a son of one of Mexico's most powerful politicians, the late Carlos Hank Gonzalez, and a frequent subject of Felix Miranda's hard-hitting columns.

Hank Rhon, now running for mayor of Tijuana, has not been charged with involvement in the killing and has repeatedly denied any link. But Zeta has run a full-page advertisement every week since 1988 asking, in Felix Miranda's name: "Jorge Hank Rhon: Why did your bodyguard Antonio Vera Palestina kill me?"

In April, Zeta ran a column under Ortiz's byline saying that the paper would not accept any political advertising from Hank Rhon because "we believe it is not ethical to give this service to someone who was the employer of the killers" of Felix Miranda.

Hank Rhon, in a written statement, said he was "profoundly saddened . . . indignant and offended" at the death of "a professional and dedicated journalist."

Ortiz was part of a joint review of the Felix Miranda case by the Mexican government and the Inter American Press Association. Ricardo Trotti, who oversees press freedom issues for the association, said in a telephone interview from Miami that Ortiz, a close friend of Felix Miranda's, was the association's representative to the investigation.

Trotti said the association had "detected irregularities" in the Felix Miranda investigation and had repeatedly asked the Mexican government to allow an independent review of the case files. At the association's meeting in March, attended by President Vicente Fox, the government signed an agreement authorizing a review of the case, and of the 1991 killing of a journalist in Ciudad Juarez.

Francisco Ortiz Franco, an editor of Zeta, had been investigating the 1998 killing of a colleague.