(Publicado en The Wall Street Journal)

On March 11, Spain suffered the worst terrorist attack in its history and one of the bloodiest the world has ever known. Terrorists planned their cowardly acts with the express purpose of killing as many people as possible, in order to sow terror and strike a mortal blow against our freedoms and rights. It was a day we felt an immense pain, pain we will never forget. But it was also a pain we must all learn from.

Its lessons are simple. If we want to stop terrorists from murdering us and from dictating how we lead our lives, we must confront them. Some think the solution is to sue for peace, to negotiate with terrorists so that they might go and kill elsewhere. But that way is unacceptable to me and to millions of Spaniards. Terrorism deserves only to be defeated. This is the debt we owe to the victims of the attacks, and to the society that mourns them.

On March 11, in a matter of minutes just after 7:30 a.m., several backpacks stuffed with explosives detonated on commuter trains on the Guadalajara-Madrid line. More than 200 people were murdered, more than 1,400 wounded, and hundreds of families destroyed forever. An entire nation was shaken to its core.

We also witnessed what’s most noble in the human spirit: the selflessness of those who rushed to help the wounded, to give blood, to offer their help in hospitals, or simply to listen to those who needed relief. We shall never forget the professionalism of emergency service workers. We don’t know exactly how many people died trying to come to the aid of other victims, but their courage demonstrates that you can find life in the midst of carnage, and that horror and fear can give way to a determination to safeguard liberty, our most precious asset.

As on any other day when we have been struck by a terrorist outrage, Spaniards had a right to the truth on March 11. Under the impact of that massacre, and in the consternation that comes from pain and fury, my compatriots deserved the honest evidence that emerged from the investigations. And that is what my government gave them.

In the hours that followed the attacks, our investigation focused on one obvious suspect, the Basque terrorist group ETA. It was a reasonable inference to make, and those who say otherwise are being either naive or dishonest. History has left us with clear evidence of ETA’s sinister habit of killing during election campaigns. The terrorists always attempt to soak our democracy in blood on the days when we Spaniards go to the polls to reaffirm our liberties.

ETA has committed more than 800 murders, among other crimes, over three decades, and has sought always to weaken and divide our democracy, which has just celebrated its 25th anniversary. A few days earlier, the group had tried to carry out an attack with 500 kilograms of explosives, one that failed only due to the intervention of the Guardia Civil, the national police. Those detained in this failed attack had a map that highlighted the zone of the Henares Pathway, through which run the trains that were targeted on March 11. And it was ETA that, on Christmas Eve, attempted another slaughter at Madrid’s Chamartin station, also thwarted by our National Police. And to continue the ghoulish catalog, the same terrorist group brought two vans loaded with more than 1µ tons of explosives to Madrid in December 1999. Once again, our security forces foiled what would have been mass murder.

My government was not alone in attributing the March 11 attacks to ETA. In the first few hours, the president of the Basque Autonomous Region, the secretary general of the Socialist Party, the general coordinator of the United Left and the secretary general of Catalonia’s Esquerra Republicana, among others, did likewise.

The only person who, in fact, publicly denied ETA’s responsibility on the morning of March 11 was the leader of Batasuna, an organization that our courts have declared illegal because of its ties to ETA. This organization is classified as a terrorist entity by both the United States and the European Union.

Nobody, then, should be surprised that during these first few hours, the Spanish government wanted to convey to its allies and friends the conviction that ETA was the group responsible for the Madrid massacre.

On the afternoon of March 11, however, the Ministry of the Interior, having been informed that an Arabic-language tape and several detonators had been found in a vehicle, ordered the opening of a new line of investigation. The ministry immediately informed the public of this.

Although ETA continued to be our prime suspect, we did not dismiss any evidence pointing elsewhere. This is what I explained in my public appearance on March 12, the day after. Apart from the tape, which was of a commercial nature and had no immediate terrorist connotation, there were only very dubious messages from groups taking responsibility. All these fragments of evidence needed to be examined with the utmost attention and precaution.

As soon as there were signs of other possibilities besides ETA, the government placed them before our citizens. On the very night of the attack, all of Spain knew what course the investigation was taking. On Saturday, Spaniards were informed of all arrests made by the police. The government revealed all that it reasonably could reveal without jeopardizing the investigations.

And yet all these efforts at transparency and disclosure were derided as manipulation by our opponents, who, furthermore, accused us of lying about what we knew. Ignoring the chronology of events, as well as the government’s efforts, some of our opponents invented a parallel reality, accusing us of a “coverup” even though the government was keeping the public informed, practically in real time, of all the evidence available and of the course of the investigation. Those who twisted the facts in this way cannot feel very proud today. Instead of backing the government during the worst crisis in Spain’s recent history, our opponents declared that truth and transparency were on their side.

Mere hours after the attacks, our investigators and security services, as well as the Ministry of the Interior, were producing results. Within only two days we had made the first arrests. Spain was in a state of shock, disoriented, in need of certitudes. It was a time to remain calm and to maintain national unity, to let the police do their work, and, most of all, to refrain from adding to the strain of a terrible situation.

But it was also the moment just before the elections, and the temptation to exploit the situation for political gain proved irresistible to some. At a time when we most needed a common front, some set out to stoke the fires of doubt. Barely had 24 hours gone by when those who were themselves lying began to accuse my government of mendacity, of a coverup, of things that would be repugnant to all good people in the context of an attack upon our country.

This wildfire of innuendo spread rapidly among many people who were justifiably indignant after the attacks. To the accusations against the government were added others by all those who had anything at all to gain from this strategy. The din was so loud, so clamorous, that nothing else could be heard above it.

Once deception had successfully supplanted truth, our opponents sought to redirect the public’s anger against the terrorists, exhorting people to channel their ire toward a government that was hard at work, a government that is still working to clarify what happened and to bring the guilty to justice. Last weekend was a time for solemnity, and for reflection. Instead, people with partisan motives scarred the moment with their screeching accusations.

In my long political career, I have been the object of the sharpest criticism, both for decisions I have taken and for those I haven’t. I’ve never been so arrogant as to fail to acknowledge those criticisms that were justified. By the same token, I’m not a coward, and I make it a point always to hit back at disparagement that has no basis.

In fact, honesty has been the essential principle of my entire political life. For this reason, but also for the respect and the loyalty I feel toward the office for which my countrymen chose me eight years ago, I want to be clear and robust: My government has told the truth. I can put up with political criticism, but I will never accept being accused of lying or manipulation. These are accusations that are intolerable, and which soil the memory of the victims. Some forget that it is this memory, and nothing else, that should be guiding our actions today.

This is what the government that I still lead has done. Others know in their hearts that they have ignored their responsibility in order to create an atmosphere favorable to their partisan interests.

Their accusations are intolerable not only because of the gravity of Spain’s present situation, but also because they destroyed the political composure that our citizens required on the day before the elections. Three days after the terrorists struck, Spaniards voted. The results of these elections are fully legitimate. Our institutions are stronger than the terrorists.

Spain is a strong nation, able to surmount the considerable problems it has encountered over the years. This is a time to remain united so that we can defeat terrorism. Those guilty of the attacks should pay for what they have done. We should not allow even a hint of a doubt that we retain the will to pursue them, wherever they are.

Spain has been one of the most active nations in the battle that democracies are waging against terrorism. This should continue to be the case. The defense of the liberties we enjoy is not just a fight for the United States or the United Kingdom to wage against their enemies. Terrorism hits wherever it can. There have been victims of many nationalities in New York, in Bali, in Mombasa, in Casablanca, in Istanbul, in Karbala–and in Madrid. No one is safe from terrorism, and no one should pretend that he is safe. Very recently, German and Dutch engineers were murdered in Iraq, for the crime of trying to lay pipes for drinking water. Terrorists have already threatened France for trying to ban wearing religious symbols in schools.

Ours is a battle between freedom, democracy and civilization, on the one hand, and terror on the other. If on September 11 we were all American, on March 11 the whole world was Spanish. Let’s maintain this spirit. We cannot just abandon this battle; it is everyone’s fight.

In the entire course of my political life, and especially during the eight years in which I have been prime minister, I have said that terrorism is not a local phenomenon, confined to particular areas or countries, to be confronted with domestic means alone. On the contrary, terrorism is a global phenomenon, one that crosses borders. And it gains in strength when we think that it is the problem of “others” and should be taken care of by “others.”

The debates that followed the Madrid attacks have been about whether they were carried out by ETA or al Qaeda. It is obviously essential to find out who was behind the attacks. But all terrorism carries the same threat; all terrorist attacks are infused with hatred for liberty, democracy and human dignity. They feed on each other.

Up until the attacks of September 11, Spain took great pains to demonstrate to the outside world that terrorism was not an isolated phenomenon, that it shouldn’t be fought by its immediate victims alone. Following the collapse of the Twin Towers, a new consciousness about the world-wide reach of terrorism finally emerged.

ETA or al Qaeda–the difference is important, to be sure, but the response to what has happened should be the same: firmness, political unity and international cooperation. Each and every democrat in the world was on those trains in Madrid. It has been an attack against all of us, against everything we believe in, and against everything we have built.

It is precisely for this reason that we must not send out confusing messages, messages that induce people to believe that we have to make concessions to those demanding that we kneel before bombs. This is not the moment to think about withdrawals of troops. And much less when the terrorists, with their message of death and destruction, have demanded that we surrender. To yield now would set a dangerous precedent that would allow our attackers to believe that they have imposed their conditions on us. It would allow our attackers to believe that they have won.

Mr. Aznar is prime minister of Spain.