In the aftermath of the Boston Marathon bombing one year ago, many commentators and public officials called this tragedy a harbinger of more homegrown terrorist attacks to come.

"We're going to see an explosion in this radicalization and recruitment," predicted U.S. Rep. Frank Wolf. "We are less secure than we were 12 years ago," claimed think-tank terrorism expert Michael Swetnam. Former Attorney General Michael Mukasey told Americans to "worry -- a lot."

To many, the Boston attack demonstrated the potency of the Islamist extremist ideology, the difficulty of detecting individuals radicalized through social media and the Internet, and the ease with which amateurs could cause massive harm in our open society.

The Tsarnaev brothers, they claimed, had paved the way for more terrorism.

While only one year has passed, much of this concern appears to have been hyperbole.

There has not been an upsurge of homegrown terrorists in the past year and there have been no copycat bombing attacks. To put this in context, over the same period there have been 14,000 murders in the United States, including 46 murders in Boston.

There also has been no epidemic of al-Qaida-inspired extremist behavior directed at American civilians.

Our research shows that in the year since the marathon bombing, there have been 15 arrests of Muslim-Americans for terrorism-related offenses, below the average of 20 arrests per year since 9/11.

Almost all of these arrests were for attempting to join a foreign terrorist organization abroad, not for planning attacks in the homeland, and were motivated by sympathies with rebels in Syria and elsewhere rather than by al-Qaida's call for Muslims to attack the West.

Our law enforcement agencies have a far more balanced understanding of the nature of the extremist threat than many of those providing public commentary after the Boston attacks.

A nationwide survey of law enforcement agencies we are conducting in collaboration with the Police Executive Research Forum shows that more than half of the agencies report little or no threat from al-Qaida-inspired extremism. Only 2 percent report the threat as "severe."

Agencies from large metropolitan areas reported somewhat higher levels of concern (27 percent reporting a low threat and 7 percent reporting a severe threat).

Overall, law enforcement agencies are treating this as a serious but manageable issue rather than the existential crisis that many have feared.

Law enforcement agencies have embraced community outreach as an effective strategy to counter violent extremism. Almost every large metropolitan police force surveyed collaborates with Muslim American communities that are targeted for recruitment by al-Qaida and related extremists.

Most of these agencies report they have established a high level of trust with the community, and two-thirds say these relationships have helped develop actionable information.

This track record contradicts claims by Rep. Peter King and others that Muslim Americans have failed to cooperate with law enforcement.

One year after two individuals inflicted pain and suffering on the streets of Boston, we should not be overly fearful or cavalier about the threat of violent extremism.

The low levels of violent conduct both before and after the Boston Marathon show that no matter how many extremist videos are posted on the Internet, the baseless ideas these videos propagate appeal to only a tiny fraction of our populace.

Yet, since small numbers of people can do so much harm, law enforcement agencies and the communities they serve must be constantly vigilant and continue to work together to prevent the next atrocity.

David Schanzer is a professor at Duke University's Sanford School of Public Policy and director of the Triangle Center on Terrorism and Homeland Security. Charles Kurzman is a professor of sociology at the University of North Carolina Chapel Hill and author of "The Missing Martyrs: Why There Are So Few Muslim Terrorists."