AUSTIN -- In a news conference Monday afternoon Austin Police Chief Art Acevedo bluntly described Larry McQuilliams.

"This man, by no means can you call him anything but an extremist. And if you look at what he did, he terrorized a city. He's just an American terrorist," said Acevedo.

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Armed with a .22-caliber long rifle and a rifle similar to an AK 47, investigators said McQuilliams shot into four buildings early Friday morning. They added that 100 rounds were shot at Austin Police headquarters, before Sergeant Adam Johnson ended the attack.

"This man took one shot from approximately 312 feet away in the dark, single-handed, while holding the reigns of two horses," said Acevedo. "He feels very strongly that there was some divine intervention."

A revelation that some would consider ironic considering police found extremist religious ideology in the van McQuilliams rented to carry out his attack. Investigators found the book "Vigilantes of Christiandom, the story of the Phineas Priesthood" which was written by a white supremacist and condemns mixing races.

"The Phineas Priesthood is really not a group or an organization at all. It is a concept," explained Mark Potok, Senior Fellow at the civil rights organization Southern Poverty Law Center. "Basically his idea is that if a person performs a so-called Phineas action, which is, meaning to murder people who have relationships across the races, then they are automatically a member of the Phineas Priesthood."

McQuilliams wrote in the book that he was a high priest.

Mark Pitcavage, Director of the Center on Extremism for the Anti-Defamation League said the last time a terrorist act was linked to the Phineas Priesthood was in 1999, so experts aren't worried about more acts based of the book. They are however concerned about a lone wolf terrorist. According to the Anti-Defamation League there have been 48 shootouts between police and extremist in the U.S. in the last five years. It's a concern Acevedo shares.

"Let me tell you what keeps me up at night. It's these guys," said Acevedo. "It's these homegrown extremist that are lone wolves, that are mad at the world, that are angry. And that's why it's important for us as Americans to know our neighbors."

Police say McQuilliams mapped out 34 places to attack, including two churches. He had the phrase "let me die" written in marker on his chest and his funeral clothes laid out on his bed at home.

He served time in prison for a bank robbery and had several other arrests in Texas and Kansas.