"Don't let anybody tell you (that) you need to give up your civil rights - your Constitutional rights - to feel safe," said Arena, a 1985 CMU alumnus who spoke Tuesday to more than 50 people in Bovee University Center Auditorium.

Arena said FBI agents have a deep respect for the Constitution instilled in them and it is their job to preserve, not circumvent, it.

Federal investigations still require demonstrated proof of probable cause, in contrast to some of media's glamorous portrayals of the FBI as a super-agency, Arena said.

"Everything we do is driven by the laws of the Constitution," he said.

The FBI has changed dramatically since he joined nearly 20 years ago, both in focus and in structure, he said.

But since Sept. 11, he said, the agency's focus has been on counterterrorism.

"The world changed Sept. 11, 2001," Arena said.

After military operations in 2002, he said, Al-Qaeda's structure and leadership was seriously damaged, but filling the void were smaller organizations and domestic radicals.

The U.S. now faces a "three-headed monster" from a re-energized Al-Qaeda and from smaller cells and home-grown terrorists, he said.

But terrorists are not the agency's only concern. The FBI faces a constant challenge of assurance within communities that feel threatened or feel their rights are being abridged, Arena said.

Though the actions of radical extremists do not represent the teachings of any doctrine, members of the Muslim community may feel targeted, he said.

"They believe the FBI's everywhere," Arena said.

But not every mosque is wiretapped, nor is every Arab under surveillance, he said. The FBI still follows probable cause in its tracking of radical extremists, he said.

Arena said the FBI depends on community members to come forward when they feel violent extremism may be developing. Trust is key, he said.

CMU Police Sgt. Chris Pryor, who attended the event, said Arena's speech showed the FBI faced many of the same community-building challenges of local law enforcement.

"It's really interesting to see at the federal level they're doing the exact same thing," he said.

Grayling freshman Richard Ryan said he felt renewed confidence in the FBI's dedication to civil liberties.

"I've taken away a great sense of security," he said.