Al Qaeda verdict

The public prosecutor describes the defendants' plan as follows: A cluster bomb would explode in the middle of a big crowd in Germany with dozens of victims, resulting in a massive bloodbath. Then the perpetrators would wait for emergency services to arrive before detonating a second bomb.

"Oh, our Sheikh, we are upholding our promise. We will begin the slaughter of the dogs," the suspected perpetrators of the so-called "Düsseldorf cell" wrote to the al Qaeda sheikh Younis Al Mauritani, who is believed to have masterminded the prospective attack. This and other incriminating e-mails containing details of what the men in Dusseldorf were planning were also found in the house of the former Al-Qaida leader Osama bin Laden in Pakistan. Mails had been saved on several computer hard drives. When US soldiers shot Osama bin Laden in his Pakistani hiding place in May 2011, they secured the hard drives and handed them over to the American security services.

How the attack was prevented

The plans of the four men in Dusseldorf must, however, have been known to the US National Security Agency (NSA) before the killing of bin Laden. The surveillance program PRISM is believed to have tracked down the al Qaeda cell in Germany, with the US tipping off German intelligence. The Federal Criminal Police Office reacted immediately. A special commission known as "Comet" kept the suspects under round-the-clock surveillance. Their phones were tapped and special programs used in order to read their e-mails.

The operation continued for some time, until the situation intensified. The men purchased a suspiciously large number of barbecue lighters, and investigators are aware that the chemical hexamine, used for making bombs, can be extracted from these lighters. Because the men were operating in a perfectly normal Düsseldorf apartment block, the investigators decided the situation had become too dangerous. They didn't want to risk the house being blown up, along with its innocent inhabitants, while bombs were being made.

On April 29, 2011 - in time to prevent a possible attack, and three days before the killing of Osama bin Laden - special federal police units (GSG9) stormed the apartment block near the University of Düsseldorf and arrested three male suspects. A fourth man, who initially escaped, was caught and arrested in December.

The suspects

The leader of the group is believed to be a 33-year-old Moroccan, Abdelabdim El-K. He is thought to have come to Germany in 2001 and to have attended a training center in the Afghan-Pakistani border region in 2010. Prior to this, he was studying mechatronics in Bochum, but was ex-matriculated in 2009.

The other suspected terrorists, like the 30-year-old German Halil S., were also working, studying, or going to school at the time of their arrest. The 23-year-old German Iranian Amid C. was still attending high school: He sat his leaving certificate in detention. The 34-year-old German Moroccan Jamil S. was an electrician.

The trial

It is not known what prompted the men to plan the attacks. They have refused to speak throughout the two years and 162 days of the trial. Nor have they responded to the question of whether the accusations against them are true. It has not been possible to question the presumed mastermind of the planned attack, Sheikh Younis, who is in prison in Mauretania. The North African authorities rejected an interrogation request and a request for legal assistance. The Dusseldorf higher regional court, which has jurisdiction in the trial, therefore had no option but to concentrate on evidence gathered by the security services and statements by other witnesses.

More than 160 people were cross-examined during the trial, including expert witnesses, FBI and German Federal Criminal Police officials, terrorism experts and intelligence service chiefs.

Defense lawyers and judge

The presiding judge, Barbara Havliza is considered to be experienced in handling cases of state security. Havliza heard the biggest and most significant terrorism trials of recent years: against the so-called suitcase bombers in Cologne, the Islamist group in the Sauerland, against members of the left-wing extremist group DHKP-C, and of the Kurdish PKK. "She's not easily fooled," say people who know her well.

The accused are being defended by Düsseldorf lawyer Johannes Pausch, who represented members of the German left-wing extremist terrorist group the Red Army Faction (RAF) in the early 1990s. It is known that Pausch decided to become a lawyer after monitoring state institutions using constitutionally questionable methods when dealing with terrorists. This is his motivation and his stance: The state must operate beyond reproach, including in cases involving terrorists. Johannes Pausch has expressed doubts that the procedures followed in this terrorism trial were beyond reproach.

Alleged procedural errors

The president of the intelligence service, Hans Georg Maassen, is said to have confirmed before the internal affairs select committee in the German parliament that the decisive tip-off about the Dusseldorf terrorist cell came from the American secret services. Later, information is also believed to have been exchanged between the police and intelligence services.

According to German law, the police and the secret services have to conduct separate investigations. Otherwise, the evidence cannot be used in court. Defense lawyer Johannes Pausch attempted to weaken the presentation of the prosecution's case by highlighting supposed procedural failures. The public prosecutor's office countered that sufficient evidence had been gathered in a constitutionally impeccable manner and without any assistance from the secret services. Where the initial tip-off came from was, it said, irrelevant to the court proceedings.

Possible verdict

Those observing the trial are assuming that the court will broadly follow the public prosecutor's argument. The fact that the barbecue lighters the men bought in fact did not contain any hexamine that could have been used to make bombs is unlikely to play much of a role.

The prosecution is calling for the accused to receive sentences of between three and nine years in prison. The presiding judge will reveal at the sentencing on Thursday whether or not she finds this an appropriate penalty.