A border militia leader on Wednesday shot and killed four people at a Gilbert home, including a toddler, before committing suicide, sources said.

Sources identified the shooter as Jason "J.T." Ready, a reputed neo-Nazi who made headlines when he launched a militia movement to patrol the Arizona desert to hunt for illegal immigrants and drug smugglers.

Massacre in Gilbert: stories, photos

Authorities have not identified the other victims, but reached by phone Wednesday afternoon, Hugo Mederos said the victims were his ex-wife, Lisa; their daughter, Amber; Amber's boyfriend, whose name The Republic is withholding until his next of kin could be notified, and Amber's 18-month-old baby, Lilly.

Mederos, who lives in Tampa, said Ready lived at the home with his girlfriend, Lisa.

Ready was a former Marine who headed the U.S. Border Guard, a militia-style group that routinely performed armed patrols in the southern Arizona desert. Early this year, Ready had formed an exploratory committee for a run as Pinal County sheriff.

In a statement of organization filed Jan. 11, Amber Mederos was listed as treasurer of the Committee to Elect J.T. Ready. Her name was nowhere to be found in amended paperwork filed March 12.

Gilbert police spokesman Sgt. Bill Balafas said the gunman's motives is unknown. Authorities recovered two handguns and a shotgun from the scene, Balafas said.

Members of the anti-terrorism task force are at the scene and providing personnel to the Gilbert Police Department, according to an FBI spokesman.

Gilbert Fire Department's hazmat team went to check on the two 55-gallon drums found on the property and determined they do not represent an immediate threat. But the bomb squad encountered munitions in the house, and a decision was made to bring in federal agents to remove them and treat them as evidence.

The shootings occurred sometime after 1 p.m. in a residential area in the 500 block of West Tumbleweed Road, near Warner and Cooper roads.

Balafas said the youngest victim was taken from the scene 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."

Balafas said the witness saw at least part of the incident.

DeAnn Rawson, 38, who has lived in the Lago Estancia neighborhood for 13 years, said she was "sick to my stomach, as you can tell everyone driving by is absolutely shocked."

Rawson stood on a street corner and answered drivers who rolled down their windows to ask what happened.

"I would have come and got her," Rawson said of the youngest victim. "It makes me mad. I can't have children, and you have other people doing things that are insane."

Gary Davis, who also lives in the neighborhood, stood outside Wednesday afternoon, watching the commotion.

"There's no excuse for taking a child's life," Davis said. "Nothing ever happens in this neighborhood. It's a shock to us."

Mesquite Junior High School, along with nearby Gilbert Elementary School, was placed on "modified lockdown" status -- meaning classes go on as normal, but students are not allowed to leave and no one is allowed to enter the building --- until 2 p.m.

Witnesses in the neighborhood said a SWAT team sealed off part of the area and that investigators told residents to remain indoors.

Nearly an hour after the shootings occurred, police were milling around the neighborhood of stucco homes with red-tile roofs. Police tape cordoned off three separate areas of Tumbleweed Road.

Republic reporter JJ Hensley contributed to the article.