The document was recently found by police, according to the Cope radio network who has seen it. It says: "those who were suprised for our quick claim of responsibility in the battle of Madrid, let them know that there were other circumstances. In the case of Madrid, the time factor was very important in order to put an end to the government of Aznar the ignoble.
Barcepundit translates the entire text of the letter, as published in Spanish in ABC and further finds this confirmation.
"Let all know that we're a part of the so-called world order. We change states, we destroy others with Allah's help and even decide the future of the world's economy. We won't accept being mere passive agents in this world"
So these guys first of all took quick credit for the bombing - so as to make it clear it was the work of Islamist extremist, which might go against their modus operandi of most Al Qaeda operations. They influence the election. Then they are brazen enough to boast to the Spanish people and the World that their actions changed the election. They not only do that, but they further insult the Spanish by throwing in that the bombing was also payback for 1492.