Mangan described the bombs as 40mm armor-piercing projectile grenades, the same type used by the U.S. military in combat. The grenades are generally fired from some sort of launcher, but Mangan said no such weapon was found at the scene.
Ready was a longtime neo-Nazi and border vigilante who authorities said walked into a house in a suburb east of Phoenix on Wednesday and killed four people, including his girlfriend and a 15-month-old baby, before turning the gun on himself.
Before the massacre, Ready led armed groups of vigilantes into the Arizona desert to hunt down what he described as "narco terrorists."
He was known to stockpile weapons and often showed off pieces of his collection for television cameras. In 2010, he distributed fliers calling for landmines to be used along the US-Mexico border as a means of stopping the flow of illegal immigration. More recently, he was raising money through his US Border Guard website in the hopes of purchasing a .50 caliber rifle and a battle tank.
Mangan said investigators were able to record the lot numbers of the grenades and will use those to try to trace where they came from. But he said the age of the explosives might make that difficult. They were at least 20 years old.
"It's sort of like purchasing a gun in a crime that was committed 20 years ago," Mangan said. "It might have changed hands several times."
Along with the grenades, investigators also discovered pyrotechnic and military style flares. But Mangan said the grenades were what investigators were most interested in.
Because the explosives were military grade, investigators called in bomb technicians from Luke Air Force Base, located west of Phoenix. The bomb techs ended up destroying the grenades at a nearby facility.