The head of one Catalan newspaper said Aznar had personally called editors to implicate ETA even when clues emerged suggesting Islamist involvement.
"The day of the massacre, Aznar told me personally, and the directors of other dailies, that ETA was the perpetrator without the slightest shred of doubt," Antonio Franco of the newspaper El Periodico said on the website of his publication.
Franco quoted Aznar as telling him: "It was ETA, there is not the slightest doubt."
Journalists at the state run news agency EFE have also demanded the resignation of their news director for swallowing the government line that ETA was behind Thursday's attacks on four commuter trains which left 200 people dead.
Subsequent evidence, notably a video tape in Arabic found in Madrid late on Saturday which claimed the blasts in al-Qaida's name, eventually pushed the media to abandon the state's line and report that Islamic groups may well have been responsible.
The surprise defeat of Aznar's conservative Popular Party to the Socialist Party in Sunday's general elections was in part put down to a public perception that the government had manipulated information about the attacks to boost its chances in Sunday's polls.
The Madrid train blasts left up to
The UN Security Council has also been severely embarrassed, having passed a resolution the day of the blasts blaming ETA for the atrocity, based on arguments presented by Spain.
The video, which has reportedly been authenticated by Spanish intelligence services, said the attacks had been carried out as punishment for Aznar's decision to back the US invasion and occupation of Iraq.
That decision was opposed by 90% of Spaniards, some of whom booed Aznar on the day of the elections and yelled "Aznar: your war, our dead".
The man who is now to replace Aznar as prime minister, Socialist leader Jose Luis Rodriguez Zapatero, said voters had turned against the government for ignoring their will concerning the Iraq war, and not because they had caved in to fear from the attacks.
A statement from representatives of the journalists working at EFE said they were demanding news director Miguel Platon step down because he "imposed... a regime of manipulation and censorship" aimed at helping Aznar's party in the elections.
"The day of the massacre, Aznar told me personally, and the directors of other dailies, that ETA was the perpetrator without the slightest shred of doubt"
Head, El Periodico
In a sharp jab, a cartoon in the French newspaper Le Monde portrayed Aznar with a Pinnochio-type nose grown long from lies from which Usama bin Ladin was swinging on a ballot box.
Aznar, who had previously announced his retirement from politics after the elections, is to stay on as prime minister during the month-long transition over to the incoming Socialist administration.
Commentators said the legacy the 51-year-old former tax inspector had hoped to leave behind will be indelibly marked by the 11 March bombings and his handling of the aftermath.