Arizona Militia Leader and Candidate for Sheriff Killed Family During 911 Call J.T. Ready founded anti-immigration militia U.S. Border Guard.

May 3, 2012 -- Anti-immigration militia leader J.T. Ready killed his girlfriend three others during a violent domestic argument as someone in the home called 911, Arizona police said today.

Police in Gilbert, Ariz., were joined by FBI agents and members of the Joint Terrorism Task Force in sorting through the carnage of the Wednesday killings.

Military-grade weapons and ammunition along with two barrels of chemicals found in the backyard have been removed from Ready's home.

"Right now we believe it's a domestic violence related situation," Sgt. Bill Balafas of the Gilbert, Ariz. Police Department told ABCNews.com.

An argument ensued inside the home J.T. Ready shared with his girlfriend Wednesday afternoon, police said.

"There was a 911 call regarding that argument. In the midst of that call, a shooting occurred. Mr. Ready shot and killed all four victims and then killed himself," Balafas said, adding that this will have to be confirmed through the medical examiner's report and forensics tests. No motive was given.

Three generations were among the dead. Ready's live-in girlfriend of two years, Lisa Mederos, 47, was killed, along with her daughter Amber Mederos, 23, and granddaughter Lilly, 1.

The body of Amber Mederos' boyfriend, Jim Hiott, 24, a veteran who served in Afghanistan, was found outside of the house near where Ready is believed to have killed himself, police said.

Balafas said forensic tests and an autopsy were being conducted.

Ready, who founded the U.S. Border Guard, a militia of armed anti-immigration activists, was running for sheriff of Pinal County and had neo-Nazi ties. He was frequently seen in photos carrying heavy weapons.

On his Facebook page touting his candidacy, JT Ready for Sheriff, Ready and his campaign often railed against Mexican drug cartels as well as illegal immigrants.

On the page today his campaign supporters said, "Reports are unconfirmed that a cartel assassination squad murdered JT Ready and several of his friends."

Police discounted the report.

Brittany Mederos, 19, heard gunshots and cries from her room as her family was gunned down, but survived the shooting.

Heather Morton, a friend of Amber Mederos, described Ready as a "control freak" on her Facebook page.

Amber Mederos served as Ready's campaign treasurer, according to a Jan. 11 filing. Ready amended the filing on March 12 and replaced Mederos with Kenneth Harris, a friend of several years.

Harris told ABCNews.com he held the job for "no more than 48 hours" and said he parted ways with Ready after the candidate refused to take his advice.

"I expect a candidate to conduct themselves in a serious way. There was a falling out," Harris said, adding that the biggest issue was poor record keeping.

He said he was unaware of the circumstances regarding Mederos' departure from the campaign and declined to speculate, other than to say he didn't believe Ready slaughtered the Mederos family.

"I do not see him ever, ever resorting to domestic violence. I don't see him ever hurting a child," he said.

An autopsy on Ready's body is scheduled for Friday, police said.