Germany's federal prosecutors have taken over the investigation into the murder of Walter Lübcke, indicating that the killing of the Kassel district president on June 2 is being treated as a politically motivated terrorist act.

If indeed the murder is shown to have been politically motivated, it would be the first such assassination on a sitting German politician since the 1970s.

Trail included death threats, weapons

A number of German outlets have reported details of the alleged far-right ties of the suspect arrested in the central city of Kassel in the early hours of Sunday morning.

The German daily Süddeutsche Zeitung reported on Monday that the 45-year-old man, named only as Stephan E., had a long criminal record, had already issued death threats via his YouTube channel, and that weapons were found during the search of his home.

According to the paper, Stephan E. had written a comment on YouTube in 2018 under his alias Game Over that read "Either this government abdicates soon or there will be deaths."

Investigators tight-lipped

Citing sources within security forces, the paper, along with public broadcasters NDR and WDR, said the suspect had been active in extreme-right groups, including the domestic neo-Nazi National Democratic Party (NPD) and a group known as the Autonomen Nationalisten (Autonomous Nationalists), a pan-European neo-Nazi group that has adopted some Antifa and far-left tactics.

Stephan E. is also believed to have been sentenced to six years in prison for an attempted bomb attack on a refugee home in 1995. He was also reported to have taken part in an attack on a trade union demonstration in 2009.

Officially, however, the federal prosecutors were giving little away about the investigation surrounding the suspect. Press spokesman Markus Schmitt appeared briefly before the cameras in Karlsruhe on Monday afternoon to confirm that the murder was being treated as a far-right extremist crime. He added that there was no indication yet that the suspect indeed belonged to a particular neo-Nazi terrorist cell, but that police were investigating whether others may have been involved.

Read more: Neo-Nazi attack survivor: 'I won't stay silent'

Neo-Nazis active in region where murder occurred

The implication of Sunday's arrest, coincidentally made on the third anniversary of the killing of British MP Jo Cox by a far-right extremist in the UK, is that the Lübcke case would mark the first time in decades that an active politician was killed by a terrorist in Germany.

The manner of the killing — a close-range shot to the head — also recalled the series of killings by the only neo-Nazi terrorist group that has so far been discovered and investigated by German security forces: the National Socialist Underground (NSU).

Over a seven-year period, the NSU carried out nine murders of people with immigrant backgrounds, using a single Ceska handgun. The last two murders happened over a three-day period in Dortmund and Kassel in April 2006.

Hendrik Puls, researcher of the far-right scene and an academic advisor to the NSU investigative committee established by the state parliament of North Rhine-Westphalia, sees Lübcke's murder in the context of the neo-Nazi scene that sprang up in the cities of Dortmund and Kassel in the mid-1990s, inspired by the British neo-Nazi group Combat 18.

"That's the first thing I thought of [when I heard of Lübcke's case]," Puls told DW. "This is a region that is tightly connected to the activities of Combat 18, both currently and historically."

In the mid- to late 1990s, Puls explained, Combat 18 and its associated groups began "propagating armed struggle," for instance by publishing magazines that included bomb-making instructions as well as sharing strategies for armed struggle.

After the NSU was finally uncovered in 2011, Puls' research with the NRW parliament led him to Kassel. "After the discovery of the NSU, the big question arose: were there supporters on the ground who might have helped? We found out that exactly at this time there were clear attempts to create a Combat 18 cell in Dortmund, and that parts of the Dortmund scene was massively armed," he said.

"The members of this Combat 18 cell all came from a group named 'Oidoxie Streetfighting Crew.' This crew included four or five people from Kassel," he added.

Xenophobia stokes extreme-right activism

Puls has also noticed that neo-Nazis became more and more vocal in the last few years, following the influx of refugees who arrived in Germany in 2015 and 2016, which led to more anti-immigrant sentiment in the mainstream political debate and hate speech on social media. As a supporter of Chancellor Angela Merkel's policy, Walter Lübke himself was on the sharp end of much of this.

"One can certainly say that the propensity for violence has certainly risen following the right-wing debates around immigration," he said. "The case of Lübcke is certainly very revealing here. Walter Lübcke faced an enormous amount of hatred in 2015. That does raise the question: how much does it take before one person says 'I'll reach for a weapon?' In certain circumstances, not much."