Most Spanish papers are in little doubt that the Basque separatist group Eta was behind Thursday's bomb blasts in the capital Madrid.
Some however are more circumspect, focusing instead on the horror of what happened.
A Basque daily roundly condemns the barbarity of the attacks, but prefers to blame Islamists.
El Mundo admits it is still not known for certain whether Eta or al-Qaeda are responsible.
Moreover, the paper says, there is a "third, if incredible, hypothesis: an alliance between Eta and Islamic terrorist groups".
But on balance it favours just one theory.
"This connection between a Marxist-Leninist group and Islamic fanatics does not seem plausible to us," it says.
The Madrid daily ABC is even more certain.
While nobody outside Spain believed a "European terrorist group with a Christian background" could perpetrate such an act, inside the country the opposite is true.
"Yesterday Eta joined the big league of international terrorism," the paper says.
"Congratulations on keeping such illustrious company. Maybe in a sacristy somewhere people are celebrating," ABC adds.
This approach is exactly mirrored in El Pais.
"Yesterday Eta killed more people than the total number of victims in their last five most bloody attacks."
The aim, the paper says, was not to scare us. "It was to terrorise us. Because terror brings paralysis."
The fact is, El Pais adds, that "Eta opted for an al-Qaeda style massacre".
"This should be borne in mind. To sow panic by making the entire population potential victims. This is the strategy."
A more open-minded view is nevertheless reflected in some papers.
"The immense tragedy seen by Spain... was marked by a lack of consensus about who had carried out the massacre," says La Razon.
"Both Eta and al-Qaeda have shown they are capable of the worst excesses," the paper adds.
Surely, it concludes, the main point is that responsibility lies with "soulless murderers whose methods are confused".
"The magnitude of the tremendous massacre perpetrated yesterday by the terrorists in Madrid, whoever was behind it, is unlike anything ever seen in the history of Spanish democracy," La Razon says.
The Barcelona daily La Vanguardia likewise says generations of Spaniards will remember what happened in Madrid.
"Victory must not be conceded to the terrorists, be they Eta fanatics, be they al-Qaeda fanatics," the paper says.
"Whatever the case, whether Eta or al-Qaeda is behind the attack, this country will never be the same again."
The Basque nationalist paper Gara is the exception in how it apportions blame.
"The massacre committed yesterday in Madrid is an inadmissible act of barbarism, whoever carried it out," the paper says.
But, it adds, "all reasonable hypotheses indicate that Islamist organisations carried out the attacks".
It insists that the attacks did not fit in with either Eta's usual modus operandi or strategy.
And it blames the Spanish government for "refusing to admit that the explosions might be the work of Islamist organisations".
This would be tantamount to admitting that the tragedy was a consequence of dragging Spain into the war against Iraq, the paper says.
BBC Monitoring, based in Caversham in southern England, selects and translates information from radio, television, press, news agencies and the Internet from 150 countries in more than 70 languages.