White supremacist and border vigilante J.T. Ready was already the subject of a federal domestic-terrorism investigation when authorities say he apparently went on a murder rampage in which he killed four people.

Federal agents seized numerous computers and munitions from the Gilbert home where Ready lived and died in an apparent murder-suicide. The FBI contacted Gilbert police and asked that their agents be involved in the investigation, James Turgal, special agent in charge of the FBI's Phoenix office, told The Arizona Republic.

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Details of federal agents' role were revealed Friday as federal search-warrant returns became available. They and Turgal's comments show that the federal government had an interest in Ready's activities unrelated to this week's murders.

A probable-cause statement attached to the search-warrant returns implies weapons seized at the murder scene were stolen from the U.S. military. Focus on those weapons could trigger a larger federal investigation.

Turgal said the FBI's domestic-terrorism investigation dated to when Ready was a member of the neo-Nazi National Socialist Movement and continued into his recent participation with a border-vigilante group. The probe is based on tips of criminal activity that Turgal would not specify.

Turgal was careful to distinguish the ongoing federal investigation from the Wednesday shootings in Gilbert that took the lives of Lisa Lynn Mederos, 47, Ready's girlfriend; Lisa's daughter Amber Mederos, 23; Amber's 15-month-old daughter, Lilly; and Amber's boyfriend Jim "Jambob" Hiott, 24.

"Yes, we did have an ongoing domestic-terrorism investigation into J.T. Ready," Turgal said, "but that has nothing to do with the horrible murders committed there."

The murders did, however, give the FBI access to Ready's documents and computers inside the home where he lived with Lisa Mederos and another of Lisa's daughters, Brittany, 19.

"Certainly, when the FBI looks at those computers, they will be interested in everything there, including other militia activity," former U.S. Attorney for Arizona Paul Charlton said.

New details also emerged in the probable-cause statement that shed light, however scant, on what authorities believe was a murder-suicide.

Documents indicate baby Lilly was shot in the head and was still clinging to life when first responders arrived at the house in the 500 block of West Tumbleweed Road, near Cooper and Warner roads.

The first 911 call came in shortly after 1 p.m. Wednesday and disconnected just after the woman caller shouted, "Oh, my God!" Earlier police statements indicate that caller was Lisa Mederos.

A second call, presumably from Brittany Mederos, told police that her mother, sister and Lilly all were shot. She not only identified Ready, 39, as the shooter, but, according to the search-warrant returns, she told a police operator that she thought Ready was trying to flee in a black Chevrolet Impala that was later found parked in the street in a direct line to the driveway of the house.

When police arrived, they found Ready and Hiott dead outside the house. There were two guns near the bodies, the report said. Turgal would not comment on whether each of the men had a weapon or if they appeared to have engaged in a shootout.

Brittany was found unharmed and locked in a bedroom, the probable-cause statement said. She later told police that she heard Ready arguing with her mother and sister and then, a few moments later, heard the gunshots.

Documents connected to the search warrant show that the FBI agents seized two computer towers and two laptop computers, correspondence, cellphones, police and Nazi uniforms, White-supremacist propaganda, bank statements and "documents w/poss(ible) co-conspirators."

Agents seized two assault-style rifles and multiple rounds of ammunition. The reporting FBI agent focused on "approximately two dozen military ordnance/40 millimeter grenades" loaded with explosives, tear gas, buckshot and smoke. An FBI bomb expert confirmed that the latter "are most likely stolen from the military as they are illegal to possess and not available to the civilian market," the agent wrote.

"On the basis of the above-described facts, your affiant respectfully submits there is probable cause to believe there is a violation of theft of government property and/or possession of illegal explosives and these items likely traveled through interstate commerce."