Other members of antitax groups, who believe in a constitutional right not to pay a federal income tax, have attacked the Internal Revenue Service in previous instances. In February 2010, a man flew a small plane into the IRS building in Austin, Texas, killing himself and one other person.
In Monday's case, though, the target was not a federal building or the IRS. This bombing at the Boston Marathon, experts say, doesn't fit with the previous attacks from Patriot Movement types.
"When you think about it, the target is not clear," said Mark Potok, a senior fellow at the Southern Poverty Law Center. "What the target was not was the government, or the IRS, or a minority group — black people, gay people, Muslims, immigrants, Latinos, and so on. It wasn't targeted at any sort of specific subgroup."
Mark Pitcavage, the director of investigative research for the Anti-Defamation League, agreed, saying this target didn't feel like the work of extreme right-wing terrorists since it had no clear connection to the government.
"The bottom line is that no domestic extremist movement, just based on their ideology alone, would have a huge reason to attack the Boston Marathon," Pitcavage said. "The prominence of the event could cause anybody from a variety of movements to carry out an attack like that."
Instead of the work of organized movements, the attack could have been the work of a single person, either someone motivated by ideology or someone who is clinically insane. Eric Rudolph, an antiabortion and antigay activist, set off bombs at the 1996 Summer Olympic Games in Atlanta that killed three people to promote his ideology.
If a domestic terrorist was involved, experts say it's likely the bomber was a part of a virulently antigovernment, antitax group that fits under the broader Patriot Movement.
People who identify with this movement aren't looking for less government or less taxation; they fundamentally believe the U.S. government has been delegitimized though a slow-boiling, malicious conspiracy. Three sub-movements clearly outline the thinking behind their violence.
Sovereign Citizen Movement: As one of the most antigovernment movements in the U.S., the Sovereign Citizen Movement believes that in the 1800s, a slow-acting conspiracy began to slowly infiltrate the federal government and replace it with an illegitimate, tyrannical government. People who follow this movement say they only owe allegiance to the original government. This movement has been blamed for several acts of violence in recent years, including the killing of two West Memphis, Ark., police officers in May 2010 by a father and son duo. Oklahoma City conspirator Terry Nichols was also a follower of this movement.
Militia Movement: Followers of this movement believe the rest of the world has been taken over by a globalist, one-world conspiracy, known to them as the New World Order. Believing the United States is the last bastion of freedom, followers stock up large amounts of weaponry and ammunition, because they think the government might one day go after their right to bear arms. Many followers of the movement liken themselves to the Minutemen who took arms against the British during the Revolutionary War. Patriots' Day, which commemorates the battles of Lexington and Concord, is an important day on their calendar.