Special Agent Teresa Carlson, head of the Federal Bureau of Investigation's Milwaukee office, said that Wade Michael Page died of a self-inflicted gunshot wound to the head. He was earlier shot by an officer in the stomach.
The FBI conducted 100 interviews nationwide with families and associates of Page, 40, a former US soldier. It has issued 180 federal subpoenas and is following 101 leads worldwide.
The authorities have recovered 139 items from the parking lot of the Gurdwara and going through email and telephone account of Page. The motive behind the incident is not clearly defined yet.
The cause of the arrest not related to the shooting and has no relation to the investigation, she said.
There was no other person involved in the incident.
Earlier, US authorities arrested Page's ex-girlfriend Misty Cook for the offence of being in possession of a fire arm as a felon.
Page was associated with white supremacists and had become a singer in so called white power band