Grimsby, Ont. was reeling Saturday after learning an American man had crossed the border and gone on a shooting spree, killing four local residents, including his ex-girlfriend, her young daughter and two grandparents, before killing himself.

Milwaukee resident Peter Kiss, 30, shot his ex-girlfriend Shannon Cruse on Friday in the driveway of a home in the small community about 25 kilometres east of Hamilton.

Police said they received several 911 calls around 9:30 p.m., after some residents heard gunshots. Authorities arrived minutes later and found Cruse, 23, lying outside with at least two gunshot wounds. She was taken to hospital but was later pronounced dead.

Neighbours said Cruse's parents lived down the street and that the door to their home appeared to have been forced open. Police then ran to the house and found four bodies in the master bedroom.

Cruse's daughter Shaniya, 6, and mother Mary Cruse, 53, were shot dead while in bed. Police said Cruse's father, Donald Cruse, 57, was also murdered before Kiss shot himself.

Neighbours told the Hamilton Spectator newspaper that Shannon Cruse had broken up with former boyfriend Kiss sometime around May 12.

According to neighbours, the two met at a trucking convention and lived together for a few months in Wisconsin before Cruse returned to Grimsby in May.

She confessed to friends that she was afraid of Kiss and told them to call police if they saw him around.

The shocking attack stunned the neighbourhood. Const. George Bench of the Niagara Regional Police said specialists were brought in to help neighbours and officers cope with the tragedy.

"Right from the outset, we knew it was going to be pretty hard to deal with, even by the most seasoned officers," he said.

Wayne Hanna, 46, who lives just doors down from one of the crime scenes, said the Cruses were a well-respected family, something that made the tragedy particularly troubling.

"(Donald) had his own business and was doing really well. And (Mary) was an excellent lady, she used to be a teacher in town. Great people," said Hanna.

"When it happens this close to home it's pretty upsetting. Nothing like this happens around here."

Investigators said they're seeking help from U.S. authorities to piece together more background on the case, including whether Kiss had a permit for the gun he used, whether he smuggled it into Canada and where he crossed the border.

"Every indication we have is that he brought the gun across the border, but we're checking on that," said Staff-Sgt. Brian Eckhardt.

Police believe Kiss left Milwaukee sometime Thursday, then drove into Canada on Friday morning in his own vehicle. He then rented another vehicle late Friday afternoon which he used to drive to the murder scenes.

The gruesome deaths come mere months after an inquest into another domestic killing east of Toronto produced sweeping recommendations designed to protect women from violent men.

A coroner's jury examining the June 2000 shooting death of Gillian Hadley, 25, at the hands of her estranged husband Ralph, produced 58 recommendations aimed at the judicial system as well as the provincial and federal governments.

In July 1998, another inquest jury made 213 recommendations regarding the systemic problems of domestic violence after hearing evidence about the shooting deaths of Arlene May and Randy Iles.