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. Last Updated: 07/27/2016

U.S. Arrests 13 Militia Members In Phoenix

WASHINGTON -- U.S. authorities said arrested members of an alleged paramilitary group had been fine-tuning explosive compounds in a plot to bomb government buildings in the Phoenix, Arizona, area.

At the same time Tuesday, officials announced another arrest on weapons stockpiling charges, bringing to 13 the number of members or would-be members of the so-called "Viper Militia," a little-known private militia, rounded up since Monday.

John Magaw, director of the federal Bureau of Alcohol, Tobacco and Firearms, said authorities had found arms caches and explosives in continuing searches of suspects' homes, including picric acid, which he described as a volatile and poisonous compound used in World War II hand grenades.

"They secured the area and we'll go back in at daylight after we've been able to confer with some other chemists and scientists and render that area safe this morning," he said on the ABC television program "Good Morning America."

According to indictments handed down on Monday in federal District Court in Phoenix, the "Viper Militia" had been training and plotting for two years to destroy buildings in the area housing the Internal Revenue Service and the Federal Bureau of Investigation, among others.

Officials said three alleged members of the group had videotaped the building housing the FBI in May 1994 with a commentary detailing how to bring it down with explosives.

Since making that tape, "what they've been doing is testing different explosives combinations," Magaw said. "How much of this chemical and how much of that chemical would make a smaller compound, yet a bigger explosion?"

Citing government scrutiny of the group during a six-month undercover investigation, Magaw said the suspects had been making fully automatic machine guns out of semiautomatic weapons.