For several years, Arizona vigilante J.T. Ready conducted armed, civilian patrols along the U.S. border, urging the use of violence to prevent smuggling and illegal immigration.

On Wednesday, the former Marine, who was running for Pinal County sheriff, went on a shooting rampage in a sedate Gilbert neighborhood, killing four people before he took his own life, authorities believe.

Massacre in Gilbert: stories, photos

The victims ranged from a 15-month-old infant to a 47-year-old grandmother. Investigators have yet to list a motive for the killing spree, but early indications suggested an explosion of domestic violence rather than a political act.

The shootings occurred at a beige, middle-class home in the 500 block of West Tumbleweed Road, near Cooper and Warner roads, a housing tract between a Methodist church and residential lakes. Friends and neighbors said the victims knew one another and all either lived at the address with Ready or had resided there until recently.

On Thursday morning, Gilbert police confirmed the identities of the victims given to a Florida relative, Hugo Mederos on Wednesday evening.

The victims were:

Lisa Mederos, 47, Hugo's former wife.

Amber Mederos, 23, daughter of Hugo and Lisa, who was employed at a nearby Wendy's restaurant.

Jim "Jambob" Hiott, 24, Amber's boyfriend, an Army veteran who served in Afghanistan.

And Lilly, Amber's 15-month-old daughter.

Hugo Mederos said his other daughter, Brittany Mederos, was at the house and heard gunfire, but was not wounded.

"She was in the bedroom when she heard the gunshots," he said, after speaking with Brittany by phone. "She heard everybody screaming. She heard the baby crying."

Sgt. Bill Balafas, a Gilbert police spokesman, said the wounded baby was taken to Maricopa Medical Center, where she was pronounced dead. "There were signs of life, that's why we transported her," Balafas said.

"This is a domestic situation. We do have a witness that our investigators are interviewing," he added, referring to Brittany.

Balafas said the three females were discovered inside the house; the two men were found outside.

Gilbert police were joined at the scene by members of an anti-terrorism task force, according to an FBI spokesman. As darkness fell Wednesday, victims' bodies had not yet been removed. Investigators retreated from the house after discovering a pair of 55-gallon drums in the backyard. Fire officials determined that the contents were not an immediate danger, but the investigation was further delayed when bomb-squad members found munitions in the house and called in federal agents.

Ready, a prospective Democratic candidate for Pinal County Sheriff, was founder of U.S. Border Guard and a member of the Minuteman Civil Defense Corps, both nationally prominent anti-illegal immigration organizations. At one time, he also belonged to the National Socialist Movement, which espouses White-supremacist theories.

On Wednesday afternoon, someone posted a message on Ready's Facebook page: "Reports are unconfirmed that a cartel assassination squad murdered J.T. Ready and several of his friends and family. ... This page's admin will keep you updated of the situation as soon as possible."

A message on the U.S. Border Guard website said members were "extremely saddened by the untimely loss of our founder" and expressed sympathy to the victims.

Ready, 39, has advocated deadly force to stop smugglers and immigrants from entering the United States illegally. He became a significant figure in Arizona politics recently because of his purported neo-Nazi views and his association with former Arizona Senate President Russell Pearce, R-Mesa, who was recalled last fall.

In a statement obtained by The Associated Press, Pearce said he befriended Ready years ago when Ready was a young man whose "attitudes and spoken opinions were good and decent," but disassociated himself after Ready "began to associate with the more despicable groups in society."

In 2008, Ready became a Republican precinct committeeman in Legislative District 18. Because of his extreme views, several GOP congressman in Arizona sent a letter to Maricopa County Republican Party leaders asking that Ready be removed from that position.

The Southern Poverty Law Center, which tracks hate groups nationally, characterized Ready as a racist and "an outright neo-Nazi" who once declared, "I firmly believe in having a minefield across the border. This is 100 percent effective."

Harry Hughes, a member of the National Socialist Movement who also took part in armed border patrols, expressed shock at Wednesday's mayhem.

"I think this is horrible," he said. "I want everyone to know J.T. Ready was the last person on Earth I'd figure to have done anything to hurt a child. It really caught me off guard. Despite all the rhetoric and the stuff we're going to hear about him being the evil Nazi, he was a good man."

Wednesday evening, Hughes was being interviewed by police, federal agents and prosecutors at his Pinal County residence in Maricopa, which Ready listed as his home address in elections paperwork that also showed Amber Mederos as campaign treasurer.

Meanwhile, a group of friends wept and commiserated at the Wendy's restaurant in Gilbert.

Heather Morton, a former employee, said J.T. Ready had worked at a nearby auto shop, met the Mederos sisters while dining at the restaurant where they worked and became involved with their mother. She said Ready moved into the family residence but was so "cruel and controlling" that Amber Mederos moved out a few months ago with her daughter and fiance.

Morton said Ready tried to boss the girls and criticized Amber's baby for being half Hispanic. "He said, 'She's 50 percent ugly,' that's how he described her," she added.

Nancy and Bud Napples, owners of the apartment complex where Jim Hiott and Amber Mederos moved, said they were a "young couple, just starting out."

Bud Napples said Hiott had been looking for work since November and recently landed a job. He watched Lilly during the day while Amber worked at Wendy's. Things were looking up for the young family, Nancy Napples said.

"They both had work, and he was so happy about that ... He had Lilly in his arms, and he was just happy."

Hiott, a member of the South Carolina National Guard, returned from U.S. Army deployment last year in Kabul, Afghanistan, where he served in an artillery unit providing security for reconstruction efforts.

Linda Hiott, a sister in Walterboro, S.C., said he was a normal guy: "He liked fast cars. He liked to go to church and go fishing."

Nancy Napples said the little girl was "a delight," with dark hair and blue eyes. "It's strange to see a couple on the verge of the rest of their lives ... and have that happen," she said. "I'm sorry for their families and the little girl that didn't really have a chance."

Police swarmed into the development known as Lago Estancia and blocked access after the slayings were first reported around 1 p.m. Footage from a media helicopter revealed at least one body lying outside.

Neighbors in the normally placid community were stunned and frightened, especially early on when it was unclear whether a gunman remained on the loose. The area was cordoned with yellow police tape while neighbors retreated into their homes, and several nearby schools were locked down.

Cathi Rand, a nearby resident, expressed outrage at the slaying of a baby. "You want to commit suicide? How dare you take children's lives."

Tammy Cowden, a neighbor who lived next to the family for about 20 years, described Lisa Mederos as "a stay-at-home grandmother who doted on her granddaughter."

"I heard the gunshots," Cowden said. "I heard three of them. ... My dog wouldn't stop growling."

"It is just horrible," added Paulie Hale. "Just really, really sad. This is a family neighborhood."

Republic reporters Jim Walsh, Laurie Merrill, Lindsey Collom, Michael Kiefer, Allie Seligman, JJ Hensley, Michelle Ye Hee Lee, Craig Harris and Gary Nelson contributed to this article.