— Terrorism charges against eight Triangle men are part of a wave of similar investigations federal law enforcement authorities have brought in recent years, according to experts.

Counter-terrorism has been the FBI's top priority since the Sept. 11, 2001, attacks in New York and Washington, D.C., said Frank Perry, who formerly oversaw the agency's Raleigh office. Every credible terrorism lead that comes into the FBI now must be disproved by an agent, he said.

"It used to be the discretion of management to decide what leads were looked at," Perry said.

Joint terrorism task forces that were formed after 9/11 have boosted investigations, he said. Previously, it was a felony for federal agents to share certain classified information with a local police chief or sheriff, he said, but the task forces allow cooperation between federal authorities and local and state agencies.

Authorities haven't disclosed how they uncovered the alleged terror plot, but investigating such cases often means using surveillance of phone lines and e-mail accounts.

Wiretaps in these cases usually require a warrant from a secret court in Washington under the Foreign Intelligence Surveillance Act. FISA sets out how intelligence on foreign agents in the U.S., including suspected terrorists, can be gathered.

"There's been a 10-fold expansion of approvals of these types of warrants since 9/11, so law enforcement has found them to be a very useful tool," said David Schanzer, director of the Triangle Center of Terrorism and Homeland Security, a joint program between Duke University, the University of North Carolina-Chapel Hill and research group RTI International.

Perry said the large increase in the number of warrants doesn't mean they are easy to get, only that more cases where they are needed are being pursued.

The U.S. Attorney's Office already has filed notices that it plans to use evidence gathered through FISA against the seven defendants who were arrested Monday.

Daniel Patrick Boyd, 39, and his sons, Dylan Boyd, 22, and Zakariya "Zak" Boyd, 20, along with Hysen Sherifi, 24, Mohammad Omar Aly Hassan, 22, and Ziyad Yaghi, 21, are expected to appear in federal court in Raleigh next Tuesday for detention hearings.

A seventh defendant, Anes Subasic, 33, has requested a Yugoslavian interpreter for his detention hearing, so it's unclear when that hearing will be held.

Federal authorities are seeking an unidentified eighth suspect in the case who is believed to be in Pakistan. A WRAL News source has identified the suspect as Jude Kenan Mohammad, 20, of Wake County.

The men are accused of trying to engage in terrorism in the Middle East and raising money, buying weapons and training in North Carolina to carry out their plan.

Schanzer, who tracks such cases nationwide, said at least 125 Americans have been prosecuted on terrorism charges in the past eight years. Two-thirds were accused of plotting attacks outside the U.S., he said.

"There's really been a constant flow of these types of cases since 9/11 scattered all over the country," he said. "These are important cases. These are potentially dangerous people. It's still a fringe element, (so) there's a small number of cases."