Ortiz was gunned down Tuesday as he sat in his car with his two youngest children, who were uninjured in the shooting. It was the third major attack against a member of Zeta's leadership since 1988.

That's when gunmen killed the newspaper's co-founder Héctor Félix Miranda. Assailants with machine guns tried to slay co-founder and publisher Jesus Blancornelas nine years later, wounding him and killing one of his bodyguards.

Both previous attacks are widely believed to have been revenge for articles published in a weekly that has routinely exposed drug lords and corrupt politicians.

After a funeral Mass at a packed church, his hearse stopped briefly outside Zeta's office, where co-workers hugged and fought back tears and security men with automatic weapons stood guard.

He was to be buried later Thursday.

The slaying was condemned by several international and local associations of journalists, who demanded that authorities do more to prevent such attacks.

On Thursday, several dozen journalists marched from the federal attorney general's office in Tijuana five blocks to the state prosecutor's office. At the end of the march, the crowd held a moment of silence, followed by a round of applause in Ortiz's honor.

Catcalls met Baja California state Attorney General Antonio Martínez Luna when he came out to meet the marchers and tell them that the investigation was ongoing.

"When they attack one of us, they attack all of us," said Rafael Morales, vice president of the Association of Tijuana Journalists. "Enough already. It isn't fair that journalists' have to pay with blood for the work of their pen or their camera." Abraham Domínguez, president of the Cartoonists' Society in Tijuana, said journalism was risky. "We are always ready to lose our lives, but it shouldn't be that way." Stuart Wilk, president of the Associated Press Managing Editors Association and vice president and associate editor of The Dallas Morning News, issued a statement saying the slaying "shocks and saddens journalists everywhere." "We applaud Mr. Ortiz Franco's crusading work, and we call for the most vigorous possible investigation and prosecution of those responsible for his tragic murder," he said.

Speaking to a group of newspaper editors on Thursday, President Vicente Fox said his administration would work with state officials to find those responsible for the killing.

"It is urgent that we take action, and with force," he said.

Zeta's editorial board has refused to speculate on who carried out the attack, and employees have declined to talk to the media.