Police were investigating the white power ties of the former US 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 9mm handgun and several magazines of ammunition — all of which had been purchased legally — and opened fire on worshippers attending a Sunday service, authorities said.
Special Agent Teresa Carlson, head of the Federal Bureau of Investigation's Milwaukee office, said the suspect — killed at the scene during a shootout with police — is now the subject of a "domestic terrorism" investigation.
"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 Centre, 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.
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.
"He was identified as a mentor for aspiring skinheads," SITE said, noting that Page "engaged in extensive online activity" and maintained user accounts on "some of the most prominent white supremacist forums".
He issued messages "urging active resistance 'regardless of the outcome'," and in posts "urged members of the forum not to leave the United States upon the implementation of policies and social developments that they opposed".
"Stand and fight, don't run," Page said, according to SITE.
The Southern Poverty Law Centre said the ex-soldier had tried to purchase goods from the National Alliance, a major US hate group, in 2000, and had more recently been the leader of the three-man hardcore punk band "End Apathy".
Photographs of the band on its Myspace webpage 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 the swastika emblem of the Nazi Party.
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.
He was a qualified parachutist who received several good conduct awards and a National Defence 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.
FBI agents and local police investigated Page's supposed address in Cudahy, a suburb of Milwaukee just four kilometres north of the Sikh Temple of Wisconsin. They said it was not booby-trapped.
In addition to the dead in the attack, 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 killings were condemned by US President Barack Obama and Indian Prime Minister Manmohan Singh, who said he was "deeply shocked and saddened".
The attack was the second massacre to shock the United States in under three weeks and may put some pressure on Obama and his rival Mitt Romney to address gun control before the 6 November presidential election.
But White House spokesperson Jay Carney said the massacre, while "horrific," would not on its own prompt a fresh administration drive for new gun control measures.
The Indian-American community in the small midwestern town was in shock after the killings, and planned to hold a candlelight vigil later on Monday.
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.
The Indian embassy in Washington said it had been told that four of the six were Indian nationals but did not respond to a request for more details.
The Washington-based Sikh Coalition said there had been "thousands" of incidents of hate crimes, discrimination and profiling against Sikhs since the September 11 attacks of 2001, 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.
Last month, a gunman burst into a movie theater showing the new Batman film in Aurora, a suburb of Denver, Colorado, and opened fire, killing 12 people and wounding dozens more.