U.S. Attorney Eric Holder, FBI Director Robert Mueller, and Homeland Security Secretary Janet Napolitano on Monday stressed the importance of cooperation between federal and local law enforcement agencies to stop terrorism. They say the recent arrest of an imam in New York, and the arrest of Najibullah Zazi and his father in Colorado, illustrate the point.

"Working together in a multi-agency, coordinated investigation, we disrupted what we believe was a plot to kill scores of Americans by detonating explosives here in the homeland," Holder said in a speech to thousands of chiefs of police gathered for the International Association of Chiefs of Police. "Every law enforcement official in America has a role to play in the fight against terrorism."

Mueller said many threats continue to come from the tribal areas of Pakistan and Afghanistan, Algeria, Somalia and Yemen.

"And we are increasingly concerned about pockets of people around the world that identify with al-Qaida and its ideology, including those who may be living here in the United States," Mueller said.

Napolitano says information that beauty supplies can be used to make bombs is being shared between law enforcement through 72 so-called "fusion centers" across the country, which collect and share information about potential terrorist activity.

"All of us now are very familiar with and are paying attention to and indeed are working with our private sector on how to coordinate, and find those kind of purchases before a bomb can be made or a bomb can go off," Napolitano said of the beauty supplies.

Later after touring an exhibit in downtown Denver meant to educate the public about terrorism and learn ways to prevent it, Napolitano said the public can also help by reporting suspicious behavior to police.

That behavior can include people taking pictures of surveillance cameras at secure buildings or stockpiling items such as fertilizer or stolen uniforms.