Also:

Informants and undercover agents were involved in almost all of the Muslim-American terrorism plots uncovered in 2012.

The National Geographic has this interview with Triangle Center Director David Schanzer today. He points out the Tsarnaev brothers:

• used a common construction for their weapon that was readily available on the internet and did not include liquid or plastic explosives,
• made no effort to leave the country,
• appear to have been poorly financed
• did not target an event that would have meaning for an international audience, and
• did nothing to publicize a political cause.

Schanzer says of homegrown terror attacks:

Since 9/11, only eleven homegrown attacks have been successfully executed (including the Boston Marathon bombing), causing 21 deaths. The vast majority of these perpetrators have been apprehended before they could engage in violence. Homegrown terrorism is an ever-present threat, but even after this horrible week, it is a manageable one.

The Global Terrorism Database operated by the START Center at the University of Maryland has the most comprehensive listing of terrorist incidents around the world from 1970 to 2011

The decade since 9/11 has seen less terrorism (of all ideologies) than other recent decades. There were 168 attacks in the ten years after 9/11, but in the 1970s, there were 1357 attacks.

Schanzer also points out:

We have not eliminated the sources of grievance at the United States that gave rise to al Qaeda and could spawn other terrorist movements in the future.

On Muslim-Americans:

Al Qaeda's ideology has been rejected by almost all Muslim Americans. Every major Muslim American organization in the United States has consistently and vociferously denounced acts of terrorism, by Muslims and non-Muslims alike.

Muslims Americans have cooperated with counterterrorism and law enforcement officials across the country. Studies show that a significant portion of the terrorism plots that have been thwarted are based on tips that have come from the Muslim American community. And many Muslim Americans are actively rebutting radical ideology within their communities, in their mosques, and on the internet.

While there is no profile of a homegrown American-Muslim terrorist.

One common strand is that many homegrown terrorists did not have a formal education and training in Islam. Their lack of this educational foundation makes them vulnerable to an ideology that claims to define the actions and beliefs of "good Muslims," but are actually contrary to the values and scripture of Islam.

Schanzer, like others, is unaware of any "precedent for radicalization of U.S.-based individuals connected to the Caucasus."

Unfortunately, the facts won't stop the bigotry and hate:

The worst of the phenomenon faced by Muslims, however, is the extraordinarily well-financed and pervasive network of anti-Islamic haters who have poisoned the dialogue about Muslims and Islam in America. This movement has enabled what ought to be fringe views held by the intolerant and bigoted few to infect the mainstream, including some elements that hold power within our political system. Muslims and those who support their rightful place as part of the American tapestry will need to redouble our efforts in light of the Boston attacks.

On a related note, UNC Professor Charles Karzner writes in the April, 2013 issue of the needlessly excessive sums Congress and the White House keep funneling to to national security:

This permanent state of emergency feeds the sense of insecurity that it is supposed to assuage. The exaggerated sense of threat degrades liberties through extended government intrusions like the provisions of the Patriot Act. The heightened concern with Islamic terrorism contributes to American fears of Muslims, who are unfairly cast into suspicion, through no fault of their own, simply by sharing the faith of extremists. The national security consensus in Washington keeps Americans scared.

Related: 9 questions about Chechnya and Dagestan you were too embarrassed to ask.

What we should be fearing is Republicans and the new assault they are launching on our civil liberties and constitutional rights, citing Boston as justification.