A second police officer shot the gunman dead. He had many tattoos, including a 9/11 one on his arm.

Milwaukee suburb Oak Creek’s Police Chief John Edwards said at a press conference on Monday that authorities believe Page was the only gunman. He used a 9mm handgun utilising multiple ammunition magazines, he added. Authorities are trying to identify another person, a White male, whom they described as “a person of interest.”

The police have identified the deceased as brothers Seeta Singh (granthi) and Ranjit Singh (raagi); gurdwara president Satwant Singh Kaleka; Prakash Singh (granthi), 39; and congregation members Subegh Singh and Paramjit Kaur. Kaleka was killed after he tried to tackle Page.

Three others are in hospital in critical condition -- Punjab Singh, Santokh Singh and police officer Lieutenant Brian Murphy. A fourth victim was treated and released from hospital.

Officer Lieutenant Brian Murphy was shot eight or nine times in the face and extremities at “very close range,” said Chief Edwards, adding that the shootings were being “treated as a domestic terrorist-type incident”.

The Southern Law Poverty Center that tracks hate crimes described Page as “a frustrated neo-Nazi who had been the leader of a racist white-power band” ‘End Apathy’. In 2010, Page gave an interview to the white supremacist website ‘Label 56’ in which he said he had been part of the white power music scene since 2000, when he left his native Colorado on a motorcycle. He attended white power concerts in Georgia, North Carolina, West Virginia and Colorado, the Southern Law Poverty Center reported.

“We are looking at ties to white supremacist groups,” said Teresa Carlson, the special agent in charge of the FBI’s Milwaukee division, at the press conference on Monday morning. The FBI is leading the investigation. “This remains an active investigation in its early stages,” the FBI said in a statement on Sunday. “While the FBI is investigating whether this matter might be an act of domestic terrorism, no motive has been determined at this time.”

A photograph of a bespectacled man, purported to be Page, on the Southern Law Poverty Center website shows him as a heavily-tattooed White male with closely cropped hair.

Special Agent Thomas Ahern with the Bureau of Alcohol, Tobacco, Firearms told ABC News the symbolism of Page's tattoos was being investigated. “And what his tattoos signified is being investigated. They are all pieces of a possible puzzle to learn what was his motive in carrying out such a horrific act," Ahern said.

The Sikh Temple of Wisconsin was founded in October 1997 with a community of 20 to 25 families. It now has 350 to 400 people in its Sunday congregations who work and live in the greater Milwaukee area. The other gurdwara is in Brookfield, Wisconsin, about 30 miles away in the northern suburbs.

US President Barack Obama said he and First Lady, Michelle Obama, were “deeply saddened” by the tragedy as he led the country in mourning the deaths of worshippers, who were arriving for the 11.30 am service. Darshan Dhaliwal, who identified himself as a leader at the gurdwara, told the Milwaukee-Wisconsin Journal Sentinel: “This is insanity.” Sikh and Muslim American organisations also condemned the incident.

At this difficult time, the people of Oak Creek must know that the American people have them in our thoughts and prayers, and our hearts go out to the families and friends of those who were killed and wounded.

— Barack Obama,  US President