Police identified the suspect as Radcliffe Franklin Haughton, 45, of Brown Deer. Brookfield Police Chief Dan Tushaus said Haughton's car had been found. ABC7's Chuck Goudie is on the scene and is reporting that Haughton's body has been found inside the spa.
Police are now gathered outside his home with a bomb squad and remote controlled robot.
The shooting happened about 11 a.m. at the Azana Day Spa, a two-story, 9,000-square-foot building across from a major shopping mall in a middle- to upper-class community west of Milwaukee.
An improvised explosive device was found at the spa, and a bomb squad was investigating, Tushaus said. Spokesmen for the FBI and Bureau of Alcohol, Tobacco, Firearms and Explosives said their agencies also had agents participating in the investigation.
The mall, a country club adjacent to the spa, and other buildings were locked down as police searched for Haughton.
Froedtert Hospital was also placed on lockdown. Several of the wounded were taken to that facility. "This is a precautionary measure, and there have been no reports that the shooter is on campus," a hospital spokesperson said in a statement. That lockdown was later lifted and the hospital resumed normal operations.
Tushaus described the situation as "fluid and ongoing," saying officers were initially focused on reaching and helping the victims.
Gina Kralik, a bartender at Red Robin Gourmet Burgers in the mall, said by telephone that the restaurant was still locked down as of about 3 p.m. She said 18 people were there -- all employees except for a couple reporters who managed to get in. She said people were allowed to leave at one point, but then the police decided not to let anyone come or go from the mall.
"We're just sitting watching the news and also trying to find out what's going on," she said.
Online court records showed a temporary restraining order was issued against Haughton in Milwaukee County Circuit Court on Oct. 8 because of a domestic abuse complaint.
Haughton appeared in court Thursday, when a no-contact order was issued and he was told to turn all his weapons over to the sheriff's department.
Beth Strohbusch, a spokeswoman for Froedtert Memorial Hospital - the hospital that was locked down - said four shooting victims were taken there, none in critical condition.
It was the second mass shooting in Wisconsin this year. Wade Michael Page, a 40-year-old Army veteran and white supremacist, killed six people and injured three others before fatally shooting himself Aug. 5 at a Sikh temple south of Milwaukee.
The shooting at the mall took place less than a mile from where seven people were killed and four wounded on March 12, 2005, when a gunman opened fire at a Living Church of God service held at a hotel.
ABC7's Chuck Goudie is in Brookfield, Wis. and will have a LIVE report coming up on ABC7 News at 5:00 PM.
The Associated Press contributed to this report.