The motive of the 45-year-old German man accused in the slaying has yet to be conclusively confirmed, Interior Minister Horst Seehofer said. However, federal prosecutors were put in charge of the case because "there is sufficient evidence for a far-right background to the crime," he said.
"A far-right attack on a leading representative of the state is an alarm signal, and it's directed at all of us," Seehofer said during a news conference in Berlin.
Walter Luebcke, a long-time member of Chancellor Angela Merkel's center-right party, was found June 2 outside his home, killed with a short-range pistol shot to the head. The 65-year-old led a regional government office in the central German city of Kassel.
The suspect detained in Luebcke's death was known to police as a far-right extremist with convictions for violent crimes dating from the late 1980s to 2009, German media reported. They include a 1993 pipe bomb attack on a refugee shelter in Germany's Hesse state.
Thomas Haldenwang, the head of Germany's domestic intelligence service BfV, said the suspect hadn't been on the agency's radar for the past decade. He said authorities can't monitor all of Germany's estimated 12,700 violent far-right extremists around the clock.
"Just as we had the category of 'sleepers' with Islamists, we have to consider such a scenario a possibility in the area of right-wing extremism," said Haldenwang.
Germany's top-selling Bild newspaper published a photo of the suspect it said was taken at a 2002 rally of the neo-Nazi NPD party in Kassel. Authorities said it was not clear if the suspect, identified only as Stephan E., was a member of the party.
Seehofer said investigators were trying to determine whether the accused man acted alone or was part of a group. The suspect actively spread far-right views on social media, according to German news outlets.
Luebcke was a target of online hate comments before and after his killing, behavior Seehofer condemned but refrained from pinning on any person or group.
Fellow politicians and extremism experts have accused the far-right Alternative for Germany party of contributing to a climate of hatred that led to the fatal shooting of a public official.
German lawmaker Michael Brand, a member of Merkel's Christian Democratic Union party, told Deutschlandfunk radio on Tuesday he saw a "direct line" between Luebcke's slaying and the anti-migrant, anti-government positions expressed by some people in Alternative for Germany.
Leaders of the party, known as AfD, condemned the killing and called for a thorough investigation. Alternative for Germany declined to confirm reports Stephan E. made a donation to the party in the past, saying it was bound by data protection and privacy laws.
The slaying evoked memories in Germany of the National Socialist Underground , a neo-Nazi group found responsible for killing 10 people between 2000 and 2007. Most of the NSU victims were immigrants. Authorities did not connect the killings to far-right activity until 2011, when two of the group's three core members died after a botched bank robbery.
Eva Hoegl, a lawmaker with the center-left Social Democrats, called on authorities to release long-classified records and take other steps to counter-right extremism that "continues to be played down."
Josef Schuster, head of Germany's Central Council of Jews, said right-wing extremists are increasingly talking about "armed struggle" and cautioned that "this should be taken seriously."
"The readiness for violence from the right must not be underestimated and downplayed," he said, saying the Luebcke slaying will be a test to see whether authorities had learned from the NSU case.
So far, the weapon used to shoot Luebcke hasn't been found, the head of Germany's Federal Criminal Police Office said.
Holger Muench said the suspect was known to have been a member of a shooting club in Sandershausen, a suburb of Kassel, but didn't own a firearms license. German news agency dpa quoted a club official saying Stephan E. was in charge of archery and the club wasn't missing any firearms.
The suspect was arrested after investigators matched his DNA records to evidence from the crime scene. He has so far refused to speak to police about the allegations leveled against him, Muench said.
David Rising contributed to this report.