Uwe Luthardt, a former senior member of Germany's far-right National Democratic Party, said he defected from the party because he did not agree with the aims of "building a Fourth Reich."
"I had joined the NPD because I wanted to do something for Germany. I wasn't interested in a greater Germany," he told Spiegel magazine. "Suddenly, everyone was saying we'll take back Silesia in Poland, and then we'll give the communists a real trashing. It was then that I realized this wasn't my world, and I left the party."
He said he was threatened by the local party boss in Jena, who told him, "One does not just leave the party. One gets kicked out or one disappears. Someone who just quits usually gets a lot of problems and can find himself waking up in the intensive-care unit."
For the NPD's part, a spokesman told ABC News, "The accusations are bold lies, nothing but lies."
Luthardt still lives in Jena, in eastern Germany, where the local party boss threatened him, but he said he was left alone after he told the party boss he knew all about the dark side of the NPD and wouldn't hesitate to talk openly about that subject.
In the interview published last week, Luthardt talked about weapons stores and how party members greeted one another with the forbidden "Heil Hitler" salute, sang banned neo-Nazi songs and relished the idea of a new Holocaust against the Jews.
"The simple aim is to restore the Reich in which a new storm trooper organization takes revenge on anyone who disagrees with them," he said.
"When you went along to evening meetings, you saw all the shaven heads, and a black sun or other Nazi symbols tattooed on their arms. They usually just boozed or were abusive. If there's no opponent around, they just fight among themselves.
"Many have an IQ close to my shoe size. Most of them are simply failures: failed pupils, people who dropped out of school or apprenticeships, alcoholics who can't find a foothold anywhere else, thugs," he said. "But every local organization has three to five men who don't have criminal records, and they are the ones sent to face the press or to man information stands."
As for the funding of the NPD, "There are still old Nazis living in South America who donate money to the party, and there are skinhead music concerts, where the bands donate their fees to the party. Last year, for instance, there was a concert with a profit of almost $20,000."
The NPD is a legitimate party that Germany tried unsuccessfully to ban in 2002. It is protected by the law that prevents the outlawing of political parties.
The failure to ban the NPD was a major embarrassment for former Chancellor Gerhard Schroeder after the discovery that important witnesses for the prosecution worked as informants for the domestic intelligence agency.
The government applied to the constitutional court to outlaw the party, "as it posed a danger to the country's constitution and democracy." The main accusations were that the NPD rejected the German constitution, scorned human dignity and fundamental human rights and tolerated neither other ideologies nor immigrants.
Many analysts believe the legal case actually strengthened the party, which has seen membership increase in recent years. The party is thought to have about 6,000 members.
The party continued marching and rallying against immigrants and foreigners, and won enough votes to enter parliament in two eastern states, in 2004 and 2006.