By the CNN Wire Staff

Oak Creek, Wisconsin (CNN) - The FBI will investigate Sunday's rampage at a Sikh temple in a Milwaukee suburb as a "domestic terrorist-type incident" that left at least six people and the gunman dead, the town's police chief said.

Another three people were wounded, including the first officer to respond to the scene, Oak Creek Police Chief John Edwards said. A second officer returned fire, killing the suspect, according to the chief.

All three of the wounded were in critical condition at Milwaukee's Froedtert Hospital, spokeswoman Carolyn Bellin told CNN. The congregation's president was among the wounded, his nephew said.

And another man told the CNN affiliate WTMJ, "Nobody's angry here. We're just confused. Was this a random act? Was this directed at us because of the way we look?"

Police did not release information about the gunman, with Edwards saying, "That is being checked into and is part of the criminal investigation." Nor would he disclose specifics of why the attack was being classified as an act of domestic terrorism.

The Sikh religion originated in northern India around 1500 and has about 25 million followers, 700,000 of them in the United States, according to the Sikh American Legal Defense and Education Fund. Because of their customary beards and turbans, Sikh men are often confused for Hindus or Muslims - and have been the targets of hate crimes since the September 11, 2001, attacks on New York and Washington, said Surinder Singh, a spokesman for the Guru Nanak Mission Society of Atlanta.