Federal prosecutors believe the main suspect, 46-year-old Stephan Ernst, was motivated by “racism and xenophobia” when he allegedly drove to Lübcke's house on June 1st, 2019 and shot him in the head.

Ernst is to appear before the higher regional court in Frankfurt alongside co-defendant Markus H. who is accused of helping Ernst train with firearms — including the murder weapon.

READ ALSO: 'A new strategy': How Germany plans to fight far-right extremism

The killing has been described as Germany's first far-right political assassination since World War II.

The trial is expected to draw huge interest but seating in the courtroom will be limited because of coronavirus social distancing measures.

Lübcke's wife and two adult sons plan to attend the opening hearing.

“Hatred and violence can have no place in our society,” they said in a statement.

“All of us who stand for a free democracy must not fall silent, but take a clear position.”

Pro-refugee speech

Lübcke, 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 during Europe's migrant crisis and spoke in favour of hosting asylum seekers in a local town.

Prosecutors believe Ernst and his accomplice attended a speech by Lübcke in October 2015 when the politician defended helping refugees and said anyone who didn't agree with those values was “free to leave the country”.

The remark was widely shared online and sparked a furious reaction from people on the far right.

After the speech, Ernst “increasingly projected his hatred of foreigners” onto Lübcke, 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 Lübcke's movements.

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

The late Walter Lübcke. Photo: DPA

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 a cache of weapons and ammunition belonging to Ernst, including revolvers, pistols and a submachine gun.

Although Ernst initially admitted to killing Lübcke, he later retracted his confession and said Markus H. had pulled the trigger.

But prosecutors maintain that while the accomplice “accepted and supported” the danger Ernst posed, he was not aware of concrete plans for an attack.

'Biggest threat'

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

But Ernst then slipped off the security services' radar, fuelling criticism that German authorities weren't 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.

READ ALSO: Four years of Germany's worst Neo-Nazi scandal

Lübcke's killing was followed by a shooting at a synagogue in Halle, eastern Germany, that left two dead in October 2019, while another gunman shot dead nine people of migrant origin in the central town of Hanau in February this year.

Several politicians have reported receiving far-right death threats in recent months, including Germany's only black MP Karamba Diaby.

Interior Minister Horst Seehofer has since declared far-right extremism the “biggest security threat facing Germany”.

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