Ralf S., 51, stands accused of 12 counts of attempted murder and causing an explosion for the attack in the western city of Düsseldorf on the afternoon of July 27th 2000. Prosecutors say he had a “racist” motive.
The accused was known to police as a right-wing extremist at the time and ran a military surplus store near the scene of the crime, which drew international condemnation.
Ten eastern European migrants – six of them Jews from the former Soviet Union – were injured in the bombing.
A 26-year-old Ukrainian pregnant woman lost her unborn child and had to undergo emergency surgery after the blast ripped off one of her feet.
Her 28-year-old husband suffered wounds over his entire body from metal fragments unleashed in the explosion and was in a critical condition for several days.
All the victims were on their way back from a German language course when the explosive, hung in a plastic bag on a fence near the Wehrhahn station entrance, went off, sparking panic.
Düsseldorf police launched a sweeping investigation, following up on hundreds of clues, more than 900 tips from the public and testimony from over 1,000 people without producing a major lead.
They had even questioned Ralf S. for several hours and placed him under surveillance soon after the bombing before determining they did not have enough evidence to arrest him.
National debate on extremist violence
Even as the criminal probe stalled, a political debate about fighting the violent neo-Nazi scene erupted.
Then interior minister in North Rhine-Westphalia state, Fritz Behrens, said it was “time for decent democrats to stand up for themselves”.
One outcome of the political controversy, and the failure of the justice system to solve the Düsseldorf case, was a movement to ban the far-right NPD party, then represented in a string of German regional parliaments.
The attempt failed when the country's highest tribunal, the Federal Constitutional Court, threw out the petition based on major procedural problems.
The criminal probe, long dormant, was only revived in 2011, after a series of 10 murders by a band of neo-Nazis.
Known as NSU, short for National Socialist Underground, the cell consisted of a trio of far-right militants who shot dead eight men with Turkish roots, a Greek migrant and a German policewoman between 2000 and 2007.
While no link was established between the NSU's killings and the Düsseldorf bombing, they spurred investigators to take the extremist threat more seriously.
A breakthrough only came in June 2014 when a prison inmate told police that Ralf S. – who was briefly in jail over an unrelated offence – had “bragged” about masterminding the attack, using an anti-immigrant racial slur.
His defence attorney, Olaf Heuvens, has sought to raise doubts about the damning testimony against him.
“Why should my client tell an inmate he barely knew something like that?” Heuvens told German news agency DPA.
However an ex-girlfriend of the defendant has told investigators that she saw in his kitchen the homemade pipe bomb, constructed using the explosives from up to six military-issue hand grenades.
Investigators say the former soldier has a swastika and a well-known Nazi fortress tattooed on his body.
Police resumed the investigation once again and last February, after Ralf S.'s release from prison, swooped on his home in a Düsseldorf suburb and took him into custody.
Prosecutors charged him in December.
Investigators say he built the TNT explosive himself and set it off using a remote-controlled detonator.
Ralf S., who denies the charges, faces life imprisonment if convicted under German law, although convicts are usually released after 15 years.
The trial is expected to last until at least July.