Try as al-Qaida might to encourage them, American Muslims still aren't committing acts of terrorism. Only 14 people out of a population of millions were indicted for their involvement in violent terrorist plots in 2012, a decline from 2011's 21. The plots themselves hit the single digits last year.

So much for a widespread stereotype. According to data tracked by the Triangle Center on Terrorism and Homeland Security in North Carolina and released Friday (.PDF), there were nine terrorist plots involving American Muslims in 2012. Only one of them, the attempted bombing of a Social Security office in Arizona, actually led to any violence. There were no casualties in that or any other incident. And the Triangle study tracks indictments, not convictions.

Terrorist incidents from American Muslims is on the decline for the third straight year. After an uptick in 2009, there were 18 plots in 2011 involving 21 U.S. Muslims. And it's not just violent plots: Fewer Muslim-Americans are getting indicted for money laundering, material support for terrorism, and lying to investigators. There were 27 people indicted on those terror-support charges in 2010, eight in 2011 and six in 2012.

"Online, there's all sorts of radical material out there – exhortations to violence, [instructions], and yet despite it being out there, so few people are taking it up," University of North Carolina sociologist Charles Kurzman tells Danger Room. Kurzman's research has been the driving force behind the Triangle study for the past four years. "From the democratization of the means of violence, accelerated by the internet, we might expect to see more violence and, fortunately, we haven't."

Chart: Triangle Center on Terrorism and Homeland Security Chart: Triangle Center on Terrorism and Homeland Security

The encouragement is indeed widespread. Al-Qaida and its sympathizers propagandize heavily online, from message boards and YouTube videos that purport to provide religious justifications for violence to the English-language magazine of al-Qaida's Yemen offshoot that offers practical advice for DIY jihadis.

Since 9/11, Kurzman and his team tallies, 33 Americans have died as a result of terrorism launched by their Muslim neighbors. During that period, 180,000 Americans were murdered for reasons unrelated to terrorism. In just the past year, the mass shootings that have captivated America's attention killed 66 Americans, "twice as many fatalities as from Muslim-American terrorism in all 11 years since 9/11," notes Kurzman's team.

Law enforcement, including "informants and undercover agents," were involved in "almost all of the Muslim-American terrorism plots uncovered in 2012," the Triangle team finds. That's in keeping with the FBI's recent practice of using undercover or double agents to encourage would-be terrorists to act on their violent desires and arresting them when they do – a practice critics say comes perilously close to entrapment. A difference in 2012 observed by Triangle: with the exception of the Arizona attack, all the alleged plots involving U.S. Muslims were "discovered and disrupted at an early stage," while in the past three years, law enforcement often observed the incubating terror initiatives "after weapons or explosives had already been gathered."

The sample of Muslim Americans turning to terror is "vanishingly small," Kurzman tells Danger Room. Measuring the U.S. Muslim population is a famously inexact science, since census data don't track religion, but rather "country of origin," which researchers attempt to use as a proxy. There are somewhere between 1.7 million and seven million American Muslims, by most estimates, and Kurzman says he operates off a model that presumes the lower end, a bit over 2 million. That's less a rate of involvement in terrorism of less than 10 per million, down from a 2003 high of 40 per million, as detailed in the chart above.

Yet the scrutiny by law enforcement and homeland security on American Muslims has not similarly abated. The FBI tracks "geomaps" of areas where Muslims live and work, regardless of their involvement in any crime. The Patriot Act and other post-9/11 restrictions on government surveillance remain in place. The Department of Homeland Security just celebrated its 10th anniversary. In 2011, President Obama ordered the entire federal national-security apparatus to get rid of counterterrorism training material that instructed agents to focus on Islam itself, rather than specific terrorist groups.

Kurzman doesn't deny that law enforcement plays a role in disrupting and deterring homegrown U.S. Muslim terrorism. His research holds it out as a possible explanation for the decline. But he remains surprised by the disconnect between the scale of the terrorism problem and the scale – and expense – of the government's response.

"Until public opinion starts to recognize the scale of the problem has been lower than we feared, my sense is that public officials are not going to change their policies," Kurzman says. "Counterterrorism policies have involved surveillance – not just of Muslim-Americans, but of all Americans, and the fear of terrorism has justified intrusions on American privacy and civil liberties all over the internet and other aspects of our lives. I think the implications here are not just for how we treat a religious minority in the U.S., but also how we treat the rights & liberties of everyone."