It was an idea born out of the Sept. 11 terrorist attacks that has grown to become the backbone of law-enforcement agencies around the country.

Next week, more than 600 members of federal, state and local law-enforcement agencies will gather in downtown Phoenix for an annual meeting that allows those participating in 77 "fusion centers" around the country to share ideas and receive training on crime-fighting and counterterrorism topics including intelligence analysis, interagency cooperation and protection of civil liberties.

Each fusion center receives information from the public and law-enforcement agencies in its region and shares the material with other centers around the country. The centers played a key role in coordinating information from different state agencies to thwart the attempted bombing of New York's Times Square in 2010 and also helped coordinate a major drug bust on Arizona's Tohono O'odham Reservation that same year.

In Arizona, employees from more than 20 agencies work at the center, housed in a nondescript brick building in north Phoenix. The federal Department of Homeland Security paid for the $5.3 million complex. Taxpayers pick up the salaries for employees, all of whom work for different federal, state and local agencies.

Next week's sessions in downtown Phoenix are closed to the public, but fusion-center administrators organizing the conference said explaining the nature of the fusion centers and assuaging concerns about civil-liberties violations are among their priorities when discussing the centers with the public.

"There are times when we get suspicious activity reported to us by law enforcement or the public, and it really is about how someone is dressing or talking or worshiping, and we push that back and say, 'That's not appropriate.' So it's an education piece as well," said Ron Brooks, chairman of the Criminal Intelligence Coordinating Council.

But the focus on protecting civil liberties while combing through the mountain of tips generated by the public and law-enforcement agencies was not always among the top priorities for some who envisioned the role of the fusion centers, Brooks said.

In the days and weeks after the Sept. 11 terrorist attacks, amid a palpable sense of fear and vulnerability, there was a movement in some circles to disregard civil liberties in the name of vigilance, Brooks said.

He concedes that some segments of the population will always view fusion centers as the "Big Brother" focused on imams and anti-government compounds, but the extensive training offered at the convention is designed to reinforce the point that police focus on how people behave, not their beliefs and backgrounds.

The centers have also become a crucial backstop to agencies facing increased budget cuts. The agencies have grown to rely on the information gathering and analysis that the federally funded fusion centers provide, said Mike Sena, president of the National Fusion Center Association.

And they're not just focused on terrorism.

Brooks and Sena work with a fusion center in the San Francisco Bay Area, which includes Oakland and one of the busiest container-shipping ports in the country. Officers at the fusion center work with officials at the port to prevent potential terrorist activity, but Brooks said they also work with police in Oakland on a more pressing issue: the city's violent crime.

"The citizens of Oakland, their daily terrorism is that violence," Brooks said. "We're worried about the al-Qaida attack, the self-radicalized homegrown extremism attack, the far-right violence, but we're also worried about everyday crime that impacts our community."

Federal funding for state, local and tribal law-enforcement agencies has decreased by 64 percent in the last two years, Brooks said. Many smaller agencies cannot afford to train or employ an information analyst to deploy their diminished resources where they're needed most.

The fusion centers can fill that void, Sena said.