The man who opened fire in a Sikh temple in the United States, killing six people, apparently died of a self-inflicted gunshot wound to his head rather than from police fire, the FBI said Wednesday.

Wade Michael Page, a singer with a neo-Nazi punk band, was initially said to have been killed by a police officer who stopped Sunday's rampage in a suburban place of worship by shooting the assailant in the stomach.

But FBI Special Agent Teresa Carlson, the head of the agency's Milwaukee office and leader of the investigation, said: "Subsequent to that wound, it appears that Page died of a self-inflicted gunshot wound to the head."

Carlson told reporters that FBI investigators have not yet established a motive for the shootings in Oak Creek, Wisconsin and have not found any evidence that anyone else other then Page was involved in the crime.

She confirmed that Wade's former girlfriend, Misty Cook, was arrested on Sunday at her home on a weapons charge but said this was unconnected to the broader domestic terrorism investigation into the temple shooting.

South Milwaukee Police and FBI agents were interviewing Cook after the earlier attack and noticed that she had a weapon despite being banned from owning a firearm because of a previous felony conviction, Carlson said.

Investigators have interviewed more than 100 people, including Page's family, associates, employers and neighbors, and were pursuing more than 100 more leads, Carlson said.

"We have conducted physical searches of his residence, his vehicle, a rented storage locker, and also space he had at a former employer.

"I want to reiterate again that after all of this work we still have identified no one else responsible for this shooting other than him. We have also not clearly defined a motive at this point," Carlson said.

The gunman, who was a singer in a so-called 'white power' band, seems to have drifted from job to job since leaving the army in 1998 and local media reported that he described non-whites as 'dirt people'.

A former army colleague recalled that Page had spoken of securing a homeland for whites.

"It didn't matter if they were black, Indian, Native American, Latin - he hated them all," Fred Allen Lucas, who served with Page at Fort Bragg military garrison, told the Milwaukee-Wisconsin Journal Sentinel.

"He criticized me for my attraction to (Latina) women," said Lucas, of Bloomington, Indiana.

"He'd call me a 'race-traitor.' He said I should change my ways because I was a blond-haired, blue-eyed white guy, and I shouldn't be wasting myself."

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 Defense Service Medal, but never won significant promotion.

The FBI, which did not have an active file on Page before the killings, has made the shooting the subject of a 'domestic terrorism' probe and Page's ties to white supremacist groups are being scrutinized.