The former U.S. soldier who gunned down six people at a Sikh temple is the subject of a "domestic terrorism" probe.
Page was a member of the Hammerskins Nation, a skinhead group.
Wade Michael Page, killed at the scene, was talking about a racial holy war before the shootings.
Police are investigating the white power ties of the former U.S. soldier who gunned down six people at a Sikh temple in Wisconsin, while the close-knit Indian-American community mourned its dead.
Wade Michael Page, 40, burst into the temple with a 9 mm handgun and several magazines of ammunition -- all of which had been purchased legally -- and opened fire on worshipers attending a Sunday service, authorities said.
Special Agent Teresa Carlson, head of the Federal Bureau of Investigation's Milwaukee office, said Monday the suspect -- killed at the scene during a shootout with police -- was now the subject of a "domestic terrorism" probe.
"We are looking at ties to white supremacist groups," she told reporters, noting that the FBI did not have an active file on Page before the incident.
"No law enforcement agency had any reason to believe he was plotting anything," she said.
But the Southern Poverty Law Center, a civil rights group, branded Page a "frustrated neo-Nazi who had been the leader of a racist white-power band," and the SITE Intelligence Group said he was an active skinhead.
A former army buddy, Christopher Robillard, told CNN that Page had spoken of "racial holy war, like he wanted it to come," but added that he never thought the suspected gunman would act on it.
Page was a member of the Hammerskins Nation, a group that describes itself on its website as a "leaderless group of men and women who have adopted the White Power Skinhead Lifestyle," SITE said in a report.
Page "engaged in extensive online activity" and maintained user accounts on "some of the most prominent white supremacist forums," SITE said, adding that he issued messages "urging active resistance 'regardless of the outcome."
The Southern Poverty Law Center said the ex-soldier had recently been the leader of the three-man hardcore punk band "End Apathy."
Photographs of the band on its Myspace webpage (myspace.com/endapathyband) showed Page with a shaved head and Gothic tattoos all over his body.
Band members were shown performing in front of extremist flags, including one bearing a swastika.
Page served as a US military "psychological operations specialist" between April 1992 and October 1998, ending his career at the base at Fort Bragg, North Carolina, home to the US Army's airborne forces and Special Operations Command.airborne
He was a qualified parachutist who received several good conduct awards and a National Defense Service Medal, but never won significant promotion.
He had a general discharge and was ineligible for reenlistment, Oak Creek Police Chief John Edwards told reporters.
US President Barack Obama said "soul searching" was needed on how to reduce violence in America after the killings, which came less than three weeks after the movie theater shooting in Colorado that left 12 dead and dozens wounded.
The new attack may put some pressure on Obama and his rival Mitt Romney to address gun control before the Nov. 6 presidential election.
The Indian-American community held a candlelight vigil late Monday at a temple not far from the scene of Sunday's carnage.
Mourners earlier packed the temple to pay their respects. Those without head coverings, including Wisconsin Governor Scott Walker, were given scarves.
"We need this," Harsimran Kaur, 30, said of the service. "It's been chaos. We have suffered so much."
The dead were identified as Paramjit Kaur, a 41-year-old woman, Sita Singh, 41, Ranjit Singh, 49, Satwant Singh Kaleka, 65, Prakash Singh, 39 and Suveg Singh, 84, all men. Singh is a common surname in the Sikh community.
Kaleka's son Amardeep hailed his father as a "hero through and through" for confronting the attacker with the only weapon at his disposal -- a blunt ceremonial knife -- and stalling his progress, perhaps saving a few lives.
Three middle-aged men, including a member of a police unit called to the scene, were reported to be in critical condition with gunshot wounds.
The Washington-based Sikh Coalition said there had been "thousands" of incidents of hate crimes, discrimination and profiling against Sikhs since the September 11, 2001 attacks, attributing blame to anti-Muslim sentiment.
Religious tradition demands that Sikh Indians wear turbans to cover their uncut hair and sport long beards, which often leads them to be mistaken for Muslims in the United States.
"I'm an American. I literally feel insecure living in the country I grew up in," said another mourner, 27-year-old Gagan Khurana.