The story of the first attack on the World Trade Centre seems at first to be little more than a bizarre tale of low farce and high tragedy belonging in a Frederick Forsyth novel. Closer study, however, leads to two important conclusions about the war on terrorism we have just declared. The first is that while we may be confident that Osama bin Laden was involved in the latest World Trade Centre attack, we cannot be remotely confident that he and his network acted alone. An attack of this complexity would have required active state sponsorship. This leads to the second point — the most dangerous state sponsor of terror is Saddam Hussein. The Secretary of State, Colin Powell, is right to contemplate a new war against him. There can be no end and no victory in the war on terrorism until Saddam is deposed.

From the moment that the first of the 1993 bombers, a Palestinian with links to the PLO, was arrested, idiotically attempting to reclaim the deposit on the rented van he had blown up, the FBI seemed convinced that this was merely a criminal matter. Since then the extraordinary investigative efforts of Laurie Mylroie, an American academic, have strongly suggested otherwise.

Mylroie argues that the original plot was infiltrated by Iraqi agents, who later disappeared, leaving the naive organisers to shoulder the blame. Her most important contribution has been to trace the movements of one agent, Ramzi Yousef, from his entry into America until his arrest almost two years after the bombing.

When Yousef was arrested he had three passports, one a temporary document under the name of Kuwait-based Abdul Basit Karim, commonly assumed to be his real identity. The evidence shows that the real Abdul Basit Karim and his family disappeared during the Iraqi occupation of Kuwait and his identity was then appropriated by the Iraqis. Almost every document about him is either missing or has been heavily doctored.

Since September 11 the world has been told that Osama bin Laden is the “Mr Big” behind the attack. This has been declared with the same certainty as the FBI claims in 1993 that no states were involved. And now, as then, the declaration ignores strong evidence of the involvement of a sponsoring state, with Iraq the most likely culprit.

There are, for example, the US intelligence reports that Muhammad Atta, one of the Sepember 11 hijackers, met a senior Iraqi intelligence officer in Europe this year. There is the scale of the attack, which would be far easier to explain were a sponsoring state involved. There are the reports of hijackers having drunken rows in bars, which is not the behaviour of Muslim fundamentalists. And there is the confusion over the identity of the hijackers, which mirrors the story of Ramzi Yousef.

So far the United States has seemed determined to fight the war on terrorism according to the so-called Powell doctrine which involves assembling the broadest possible coalition for the narrowest possible objectives. At the end of the Gulf War the Powell doctrine helped President Bush to decide against invading Iraq and deposing its dictator. Now the pressure exerted by Arab coalition partners is to confine the war to Afghanistan and to ignore Iraq.

Giving in to such pressure would be to repeat history’s mistake. Even the author of the Powell doctrine himself may be ready to agree. Whatever its role in the latest atrocity, Iraq is clearly a sponsor of international terrorism. The evidence that it is assembling biological, chemical and other weapons of mass destruction is overwhelming. Its willingness to invade its neighbours and lay waste to countries is already proven.

Leaving President Saddam Hussein in power is leaving a primed bomb under the democratic world. Any victory we claim while he still rules in Baghdad is no victory at all.

daniel.finkelstein@thetimes.co.uk