In addition to the three people killed in the shooting at the Azana Salon and Spa, a long-established shop in a busy suburban commercial district near a mall, four women were injured in the shooting, the authorities said. None of the victims had been publicly named as of Sunday evening as the authorities sought to positively identify them and to notify family

The gunman, whom the police identified as Radcliffe F. Haughton, 45, a resident of Brown Deer, also died inside the spa, apparently of a self-inflicted gunshot wound, the police said. The shootings appeared to stem from a domestic dispute, painfully documented in weeks of police reports and court orders, between Mr. Haughton and his estranged wife, who witnesses said was employed at the salon.

"Today's action was a senseless act on the part of one person," Mayor Steven V. Ponto of Brookfield said somberly late Sunday. He quickly added, "Try as we might, these can't be avoided."

Residents largely view the Milwaukee suburbs as safe and relatively removed from the worries of urban life. "This doesn't happen in Brookfield," said Christine Carpenter, 24, who works at a drugstore not far from the spa and on Sunday evening was still trying to grasp what had happened. "You think good neighborhood, good schools — this stuff doesn't happen to us."

In fact, however, in recent years in the Milwaukee suburbs, there have been other such attacks, including a shooting less than three months ago in which a self-proclaimed white supremacist named Wade M. Page opened fire in a Sikh temple in Oak Creek, Wis. In 2005, here in Brookfield, less than a mile away from the day spa, a gunman killed seven people, including two teenage boys, at an evangelical church meeting, and later killed himself.

The shooting, the authorities said, began shortly after 11 a.m. Central time, sending staff members and barefoot clients fleeing into parking lots and businesses. Witnesses described a panicked scene of bloodied women and confused passers-by who, at least initially, could not understand what had occurred, even as at least one person was seen crying, according to witnesses, and screaming out to passing cars.

"Everybody was keeping calm, but we were all confused about what was going on," said Joe Brent, 27, of Minneapolis who said he had been in a McDonald's next door to the spa when he heard a gunshot. Almost immediately, said Mr. Brent, who was in town for a job interview, a police officer entered the restaurant and ordered everyone out.

As he was leaving the McDonald's, he said, he saw a woman in her 20s leaving the salon, holding a paper towel to her bleeding neck as a police officer escorted her to an ambulance.

"It was pretty bad," Mr. Brent said. "I was surprised that she was able to walk."

He said he then saw officers carry two more women from the salon and put them on stretchers, he said.

Four women — between 22 and 40 years old — were treated for gunshot wounds at Froedtert Hospital, officials at the hospital said. Several had undergone surgery or were expected to soon, the officials said.

As the authorities carried victims away, Police Chief Daniel K. Tushaus said, they faced another problem: they were uncertain where the gunman was, and came upon something that initially appeared to be an improvised explosive device inside the spa — presumably left by the gunman.

The possibility that the gunman might still be loose set off new chaos, leading the authorities at the hospital where victims were being treated to put the entire facility on lockdown, preventing routine visitors from even entering the building. For hours, highway exits near the spa were closed down, some stores in the nearby mall were shut, and police officers from around the region all but filled the area.

Steven Yaccino reported from Brookfield, Wis., and Monica Davey from Chicago. Michael Schwirtz and Marc Santora contributed reporting from New York.

This article has been revised to reflect the following correction:

Correction: October 21, 2012

An earlier version of this article mistakenly referred to the suspect, Radcliffe F. Haughton, as Mr. Radcliffe on second reference.