Leading article: Trials that demonstrate our strength

However much the intelligence services and the police may be criticised for their excesses, it should never be forgotten that thwarting terrorist conspiracies is an extremely difficult job. Suicide terrorism is a unique offence in that the police cannot arrest perpetrators after the event. We, the public, demand that these attacks are disrupted before they take place.

That poses the question of how to prove an "intention" to commit mass murder in a court of law. Terrorists rarely put down their plans on paper to make life easy for prosecutors. If the security services wait too long for a watertight case to be built, it might be too late. And such evidence may never arise. Those who have analysed the cases of extremists who went on to become suicide bombers in recent years are often hard-pressed to come up with any evidence that proves unequivocally that an atrocity was being planned. No wonder the Government and the police often resort to locking terror suspects up without charge or placing them under control orders, rather than risk a trial.

That is the context in which we should consider the decision by the Court of Appeal yesterday to quash the conviction of five British students found guilty last year of possessing material for the purposes of terrorism. In this instance, the authorities went down the correct route. The police were alerted after the parents of one of the men found a note by their son hinting strongly at impending "martyrdom". They built a case against the group, gathering evidence of their possession of terrorist literature and presenting it before a jury. The Court of Appeal argues that the jury was misdirected and that, offensive and inflammatory as the material might have been, there was no evidence of an actual attack being planned. This seems to be the right outcome.

But that cannot be the final word. As well as respecting the decision of the Court of Appeal, we should recognise that the Crown's case was not a hopelessly weak one. The material that these men had gathered and exchanged is precisely the sort of propaganda that has been used to radicalise and groom those who have gone on to commit acts of suicide terrorism. Moreover, it is incumbent on those who resist detention without trial on civil liberties grounds to support efforts by the authorities to pursue terror suspects through the courts. Not all prosecutions will be successful, as in this case. But prosecution, not internment, has to be the goal. The right to an open trial must be defended, even in the face of the nightmarish threat of suicide terrorism.