BOSTON - In the aftermath of the Boston Marathon bombing, which cost the life of at least three people and injured nearly 180 others, there are more questions than answers. Who plotted the worst attack on U.S. soil since 9/11? What was the motive of this “terrorist act,” as U.S. President Barack Obama defined it?

So far, investigators have been unable to identify the author or authors of the bombings, set off with 6-litre pressure-cookers filled with explosives. All hypotheses remain open.

Is it an isolated extremist act like the one of Anders Breivik, perpetrator of the carnage in Norway in 2011? Is it an operation of Al-Qaeda or its associates? In the American press, the first temptation was to assign the attacks to Islamists. A 20-year-old Saudi student injured in the blasts was reported to be a suspect, but the police now consider him a witness instead.

Indeed, there are a significant number of specialists who suspect right-wing extremists affiliated with the so-called "Patriot" movement could be behind the attack.

The Boston bombings took place on “Patriot’s Day”, a civic holiday commemorating the anniversary of the battles of Lexington and Concord on April 19, 1775. It was also “Tax Day”, the date when all Americans must pay their annual tax bill. Thus patriot groups, which consider the federal government their No. 1 enemy, could have chosen this date for symbolic reasons.

Security officials also note that April 19 will be the anniversary of the deadly Oklahoma City bombing of 1995, carried out by Timothy McVeigh, who was affiliated with the movement. The attack, which left 168 dead, occurred during a period when anti-government movements were on the rise following a ban on assault rifles voted in 1994 during the presidency of the Democrat Bill Clinton.

The Obama factor

At the beginning of March, the Southern Poverty Law Center (SPLC) published a “Hate And Extremism" report, which included some troubling findings. In 2012, the U.S. counted 1,360 patriot groups, a 813% rise since the election of the first black president of the United States, Barack Obama, in November 2008.

These movements are convinced that the American federal government is about to impose “martial law in the U.S.” They are often quick to come up with conspiracy theories to explain the decisions taken by Washington. The Oath Keepers, a patriot movement formed by ex-military personnel warns in a "message to the oath breakers and traitors": "We will never disarm.”

The arrival of an African-American president to the White House revived the Patriot movement. Many topics currently in discussion in Congress feed their hatred towards the government and its representatives. On Tuesday, eight senators introduced a landmark bill aimed at reforming the nation's immigration policy. In the virtually all-white patriot circles, such moves are seen as further ceding to the on-going demographic changes. By 2043, Whites will no more be a majority.

The push by the White House and a part of Congress to tighten regulations of firearms after the Newtown tragedy in December has sparked heated reactions in the patriot circles. They think that the government has only one objective: taking away their guns. After the re-election of Obama in November, hundreds of thousands of Americans signed a petition demanding their state government to secede.

The warning from the Southern Poverty Law Center was confirmed by a recent study published by the West Point’s Combating Terrorism Center (CTC), which tallied all the right wing extremist attacks between 2000-2010: the strikes were a four-fold increase from the 1990s. The CTC had already warned Washington once about the growth of the internal terrorist threats -- just before the Oklahoma City bombings.