Whatever caused Wade Michael Page to massacre worshipers at a Wisconsin Sikh temple on Sunday may never be known. But this much is clear: For at least a decade, he had been steeped in a neo-Nazi “hate music” scene that espouses white power and racial superiority and occasionally promotes violent acts against people of other races and religions.

The existence of this music subculture surprised many Americans, but law enforcement agencies and civil rights organizations that monitor hate groups have been paying attention to these groups and their followers since the genre began to emerge in the United States in the early 1980s. The Anti-Defamation League estimates that there are approximately 100 to 150 active or semi-active bands that perform and release such music in the United States.

Aiming to energize followers and intimidate others, many of these bands boast names that favor shock over subtlety — Jew Slaughter, Grinded Nig, Angry Aryans, Ethnic Cleansing. Page, a guitar player and singer, was once a member of 13 Knots, a name that refers to the number of knots in a noose.

“The main theme of these groups is to create anger and direct it toward perceived enemies: Jews, blacks, other minorities,” says Mark Pitcavage, director of investigative research at ADL, who has been tracking hate music since the early 1990s. The music, he adds, is also intended to “create a group sense, praising or glorifying skinheads or white supremacists like themselves.”

The music these bands play takes various styles, but the most prevalent are racist variations of some of rock’s most aggressive forms, such as Oi!, an early punk style that emerged in Britain in the 1970s; hard-core punk; and death metal, a particularly bludgeoning style of heavy metal punctuated by storming guitars and guttural howls.

Wade Michael Page, seen in this undated picture from the MySpace page for End Apathy, was a founder of that band. (Myspace.com/via REUTERS)

Concerts and festivals are held periodically across the country, the most well-known of which is Hammerfest, a concert put on by the Hammerskins, a white supremacist skinhead organization that is actively involved with white power music. (Although many followers of white power bands are commonly called skinheads, there are also skinheads who are anti-racist. They are often referred to as SHARPs, which is short for skinheads against racial prejudice.)

End Apathy, a band that Page founded, had released songs on a Maryland-based record label, Label 56, that also distributed recordings by dozens of white power bands from the United States and Europe, including such groups as Bound for Glory, Luftwaffe Raid, Youngland, Skrewdriver, Definite Hate, Children of the Reich and Stormtroop 16.

Page may have been involved in organizing and promoting a white power concert in March in Richmond, according to postings on Stormfront.org, one of the most active white supremacist online forums, made by a person under the name End Apathy.

On its Web site Monday, Label 56 distanced itself from the Wisconsin shooting and removed all End Apathy content. One of the label’s owners, Clemie Richard Haught Jr., did not respond to multiple requests for comment. A statement on the label’s Web site said: “please do not take what Wade did as honorable or respectable and please do not think we are all like that.”

But many fans of white power music aren’t backing away from the genre.

“If my art form is responsible for this shooting, how come no other art form is responsible in all of the other shootings?” asks Byron Calvert, a white power music producer and supporter. “The n------ are always rapping about killing white people, but no one complains about that.”

Calvert owns Tightrope Records, a Melbourne, Ark.-based store and Web site that sells white power music and racist materials, including Hitler party balloons, white power T-shirts and stickers that say “Fight Crime Abort Black Babies.”

The music appeals to its followers, he says, because “they are tired of multiculturalism being shoved down their throats. They’re tired of the forced guilt trip about slavery. They’re tired of black people making money singing about beating up white hos.”

And while the scene is relatively small, he says that it has more support than most people think since most sales of the music take place online.

“It’s a niche market. You don’t go to Wal-Mart to buy white power music.”

Calvert also says that many fans of the music don’t stand out.

“The cartoon caricature of a white power music fan is someone who is tattooed and has a felony record,” Calvert says. “But that’s circus s---. Our customers, you couldn’t pick them out of a crowd. They are the captain of the football team, the cheerleaders, just regular suburban kids.”

Although some hate bands are more popular than others, the concern for people such as the ADL’s Pitcavage is that the scene exists at all.

“There is violence inside the scene itself and to some degree they seem to directly inspire violence after their concerts,” he says. “But many of these groups also condone violence as a solution to a wide variety of problems. They spread hate and violence across society.”

Frequently, white supremacist groups have used the music as a recruiting tool. At one point, Resistance Records, a label based in West Virginia, was reported to have $1 million in annual sales, although researchers say the distribution has fallen off in the past several years.

And James W. von Brunn, the white supremacist who killed a guard at the U.S. Holocaust Memorial Museum, once said he was “very, very interested in the potential for Resistance Records to bring in a new generation of supremacists who were a cut above the knuckle-dragger types,” Todd Blodgett, who was a Resistance Records co-owner, told The Washington Post in 2009.

In 2004, white power music label Panzerfaust Records of Minnesota organized Project Schoolyard, a project to get white supremacists to distribute free white power music compilation CDs to high school and middle school students. In subsequent years, after the demise of Panzerfaust Records, other white supremacists attempted several similar efforts under various names.

Project Schoolyard 2’s compilation disc included such songs as “White Pride, White Passion” by Brutal Attack, “White Revolution” by RAHOWA (Racial Holy War) and “Some N------ Never Die” by Johnny Rebel.

Project Schoolyard was one of the attempts to use the music for recruiting purposes but generally those have been limited and not very successful, Pitcavage says. “The message is essentially one of hate,” he says, “and there’s not a lot of positive response to that.”

Jill Garvey, associate director of the Center for New Community, a Chicago-based civil rights organization, says she worries that the Wisconsin shooting may spark renewed interest in hate rock bands. In 1999, the center launched Turn It Down, a campaign to counter white power music and its growing influence by educating communities about how to respond to the music and its followers. The campaign has operated intermittently since then, but Garvey said Tuesday that the organization is considering reactivating it. One of the center’s biggest efforts, she said, has been to engage sites such as MySpace and Facebook to deactivate accounts that are promoting white power music.

“We’re seeing that this might reignite some interest, both from the public and from those involved with the music,” Garvey says. “Once the controversy in the press dies down, there may likely be a resurgence in using the music as a way to recruit new followers.”

Such music, however, is well within the tradition of protected free speech in America, says an expert in First Amendment law. The bar is high for finding hate speech unlawful, says Eugene Volokh, a law professor at the University of California at Los Angeles.

“That’s true whether it is extremist Islam or pro-anarchist literature or the communist manifesto or extremist animal rights groups,” he says. “And it’s true for extremist racists as well. Speech is protected unless it is intended to, and likely to, produce imminent violence or other illegal conduct.”