Suspect Stephan E. has admitted to the killing of conservative politician Walter Lübcke, Federal Prosecutor General Peter Frank told members of Germany's parliament on Wednesday morning.

Head of a regional government in the city of Kassel, Lübcke was found dead outside his home with a gunshot wound to the head on June 2. The 65-year-old was a member of Chancellor Angela Merkel's conservative Christian Democratic Union (CDU).

Stephan E. said he acted alone, according to Bundestag member Ulla Jelpke, who spoke to DW after a special hearing of the parliamentary interior affairs committee, at which the heads of various security forces and Interior Minister Horst Seehofer briefed Bundestag members.

But despite Stephan E.'s claims, Frank said investigations into possible accomplices are ongoing. Stephan E. is believed to have had connections with a number of far-right organizations, including the militant Combat 18, the National Democratic Party (NPD), and the neo-Nazi group the Autonome Nationalisten (Autonomous Nationalists).

"Of course we're assuming he wants to cover others," Jelpke, of the socialist Left party, told DW. "As you can imagine, investigations are taking place." Last week, the taz newspaper reported that a neighbor had seen two cars speeding from the scene of the crime.

Irene Mihalic, who represented the Green party on the committee, told reporters after the hearing that the authorities now had to "turn over every stone" to investigate the killing, and uncover any potential network out of which the suspect acted.

Lübcke: A far-right target

News magazine Der Spiegel reported that Stephan E. told police the killing was triggered by remarks made by Lübcke during a townhall meeting in October 2015, on the creation of a new refugee reception center.

Facing hecklers during the meeting, Lübcke said: "It is worth living in our country. Here you must stand up for values, and whoever doesn't stand up for these values can leave this country any time if they don't agree with them." Some media reports also said Stephan E. attended the meeting himself, but that has not been confirmed.

A video of Lübcke's remarks quickly spread in far-right circles, and was referred to in speeches at anti-immigration PEGIDA demos in 2015 and 2016. Lübcke subsequently received a number of death threats, and during the hearing Frank described Lübcke as a "provocative figure" for the far right.

Read more: Opinion: German politician's murder is an attack on democracy

DNA evidence and confession

In the weeks following Lübcke's killing, authorities concluded that it was motivated by right-wing extremism and arrested Stephan E. after finding DNA evidence linking him to the scene.

Frank also told the committee that the 45-year-old's flat had been searched again, and more evidence was collected, though the murder weapon, believed to be a 9 mm handgun, has not yet been found.

Since his arrest over a week ago, various news outlets have uncovered evidence of Stephan E.'s connections to the neo-Nazi scene and his own far-right sympathies. Photos have surfaced of him with members of the militant neo-Nazi group Combat 18, taken in March, though the identification has since been cast into doubt by Spiegel TV.

Stephan E. has previously been convicted for violent attacks on migrants and left-wing sympathizers. These included the stabbing of a migrant in 1992, and the attempted pipe bombing of a refugee shelter in Hesse in 1993. He was also involved in a neo-Nazi attack on a trade union demo in 2009.

At Wednesday's hearing, Thomas Haldenwang, head of Germany's domestic intelligence agency, the BfV, said Stephen E. had not appeared on the agency's watchlist in the past decade.

Read more: Far-right AfD 'complicit' in German pro-migrant politician's killing

Lübcke was found shot dead on the terrace outside his home

Terror network and NSU connections

Jelpke was critical of the BfV, saying it was inexplicable that the agency, which tracks extremists, had had no active file on the suspect. "It couldn't even be confirmed whether [the agency's] office in Hesse had a file," she said. "[Haldenwang] didn't know if there was a file ... Stephan E. appears to have gone out of sight, out of mind, so to speak."

"I get the impression they're trying to investigate with some urgency, but at the same time they're hitting their own boundaries, because for years they didn't acknowledge the phenomenon of terrorism in far-right extremism," she added. "And they've admitted that now, more or less."

Jelpke and Mihalic also called on authorities to investigate any possible connection to the National Socialist Underground (NSU) murders. The neo-Nazi cell, uncovered in 2011, killed the last of its nine victims of migrant background, Halit Yozgat, in an internet cafe in Kassel in 2006 — also, as in Lübcke's case, with a close-range shot to the head.

One of the initial suspects in Yozgat's murder was Andreas Temme, an agent of the state intelligence agency in Hesse, who was present in the internet cafe at the time of the killing. As Jelpke pointed out, the state intelligence agency in Hesse answered to Lübcke's office.

"If Stephan E. was active at a time when the NSU was murdering people, there must be further connections, which will be brought to light now," said Mihalic. "Maybe the story of the NSU will have to be written again."

Interior Minister Seehofer, who expressed his shock at Lübcke's killing, promised that the murder would be investigated fully. He added that the ministry would assess whether to ban Combat 18.

Hundreds of people gathered in Lübcke's home town of Wolfhagen on Saturday for a vigil honoring his life. Thousands of people also joined protests against right-wing violence in Kassel and other German cities over the weekend.

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Editor's note: Our initial version of this story incorrectly stated that the suspect confessed as his trial began. The trial is yet to start. He has handed a confession to investigators.