A German neo-Nazi went on trial Tuesday for the murder of pro-refugee politician Walter Luebcke, a killing that shocked the country and highlighted the growing threat of right-wing extremism.

Federal prosecutors say the main suspect, 46-year-old Stephan Ernst, was motivated by "racism and xenophobia" when he allegedly shot Luebcke in the head on June 1, 2019.

Ernst appeared at the higher regional court in Frankfurt alongside co-defendant Markus Hartmann, who stands accused of helping him to train with firearms -- including the murder weapon.

The killing is believed to be Germany's first far-right political assassination since World War II.

Some people queued all night to get into the court but seating was limited because of coronavirus social distancing measures.

Both defendants wore face masks as they were led into the courtroom, where they took their seats between plexiglass screens installed to curb the spread of COVID-19.

Luebcke's widow and his two adult sons also attended the opening hearing.

"The family wants to send a clear signal against hatred and violence," their spokesman Dirk Metz told reporters.

The words 'Human dignity is inviolable' stand above the entrance to a court room at the Higher Regional Court in Frankfurt, where Stephan Ernst will stand trial
The words 'Human dignity is inviolable' stand above the entrance to a court room at the Higher Regional Court in Frankfurt, where Stephan Ernst will stand trial AFP / THOMAS KIENZLE

Luebcke, 65, belonged to Chancellor Angela Merkel's conservative CDU party and headed the Kassel regional council in the western state of Hesse.

He supported Merkel's 2015 decision to open the country's borders to refugees and spoke in favour of hosting asylum seekers in a local town.

Prosecutors believe Ernst and his accomplice attended a speech by Luebcke in October 2015 when the politician defended helping refugees, adding that anyone who did not agree with those values was "free to leave the country".

The remark was widely shared online and turned Luebcke into a hate figure for the far right.

After the speech, Ernst "increasingly projected his hatred of foreigners" on to Luebcke, prosecutors said in the indictment.

Following mass sexual assaults by migrants against women in Cologne on New Year's Eve 2015 and a 2016 Islamist attack in the French city of Nice, Ernst allegedly began tracking Luebcke's movements.

There was a heavy security presence at the court
There was a heavy security presence at the court AFP / THOMAS KIENZLE

Between 2016 and 2018, prosecutors say he worked with Hartmann to improve his skill with firearms, and the two attended right-wing demonstrations together.

In the course of their investigations, prosecutors separately charged Ernst with attempted murder for allegedly stabbing an Iraqi asylum seeker in the back in 2016.

They also uncovered weapons and ammunition belonging to Ernst, including revolvers, pistols and a submachine gun.

Although Ernst initially admitted killing Luebcke, he later retracted his confession and said Hartmann had pulled the trigger.

But prosecutors maintain that while Hartmann "accepted and supported" the danger Ernst posed, he was not aware of concrete attack plans.

Ernst has a long criminal history and was known to police as a neo-Nazi sympathiser.

He was convicted of an attempted bomb attack on an asylum home in 1993. In 2009, German media say he took part in neo-Nazi clashes targeting a union demonstration.

But Ernst then slipped off the security services' radar, fuelling criticism that the authorities were not taking the far-right threat seriously enough.

German police came under fire years earlier for overlooking racist crimes after it emerged that a neo-Nazi terror cell, the National Socialist Underground, had killed 10 people, mainly immigrants, between 2000 in 2007.

In October 2019, just months after Luebcke's death, Germany was rocked by a shooting at a synagogue in the eastern city of Halle that left two dead. The suspect later admitted to anti-Semitic and far-right motives.

Last February, another gunman shot dead nine people of migrant origin in the central town of Hanau.

German President Frank-Walter Steinmeier, speaking at an event in Berlin on Tuesday, urged people to actively take a stand against discrimination and intolerance.

"It's not enough not to be racist. We must be anti-racist," he said, adding that this must be "learned, practised and lived".

Interior Minister Horst Seehofer recently declared far-right extremism the "biggest security threat facing Germany".

He has promised tougher security measures, including a crackdown on online hate speech.