A Spanish parliamentary commission to investigate the Madrid train bombs that killed 191 has held its first meeting.
Aznar may be questioned during the commission hearings
The commission has two months to establish the exact course of events between the 11 March bombings and the general elections three days later.
The commission has the power to call anyone to be questioned, including former Prime Minister Jose Maria Aznar.
The 16-member commission has been given a broad mandate to satisfy the demands of all Spain's main political parties.
The Spanish Socialist Party (PSOE) spokesman, Diego Lopez Galido, says the aim is to make sure a catastrophe like 11 March never happens again.
Ten bombs exploded on four trains in and near Madrid's Atocha station during the busy morning rush hour on 11 March, days ahead of a general election.
The BBC's Danny Wood, in Madrid, says that since the train bombings and the surprise election win by the Socialist Party on 14 March, there has been a heated debated across Spain about the events surrounding the train bomb attacks.
The conservative government in power on 11 March initially blamed the Basque separatist group Eta for the attacks.
When reports started to emerge that the Islamic militants were probably behind the bombings, the Socialists accused Mr Aznar's government of a cover-up.
Three days later they swept to an unexpected election victory under Jose Luis Rodriguez Zapatero.
The investigating panel of 16 MPs are expected to use the first of the closed-door sessions to establish the list of those who they would like to question and when.
They are also expected to discuss what documentary evidence they would like to see.
The leader of the conservative Partido Popular (PP), Mariano Rajoy, says his party has nothing to hide.
He says the Socialists used the attacks to manipulate public opinion before the general election.
The PP has told Spanish news agency Efe that it will not oppose the appearance of Mr Aznar, if he is called to a hearing by the commission.
After the first meeting on Wednesday, the head of the commission, Paulino Rivero, said that he was very happy with the atmosphere of the opening meeting.
On Tuesday, a Spanish judge investigating the train bombings freed three Spaniards held on suspicion of helping the Madrid train bombers obtain explosives.
He kept five others under arrest for further questioning.
There are already 14 others under arrest in connection with the attacks.