The case involving Hosam "Sam" Smadi and the government’s claim that he wanted to blow up a Dallas skyscraper is the latest in a long line of terrorism cases with ties to North Texas.

The trail goes back to the 1970s, when supporters of the Irish Republican Army allegedly smuggled guns through the Metroplex. In 1994, Timothy McVeigh drove to Ennis to buy the fuel for the bomb he would detonate in Oklahoma City.

Wadih el Hage, Osama bin Laden’s personal secretary, was living and working in Tarrant County when he was arrested for involvement in the 1998 bombing of two U.S. embassies.

And on Friday, a man arrested last month in Arlington, Texas, was charged with attempted arson in California in what investigators believe may be a case of environmental terrorism.

"There has been enough activity that Dallas is not considered a hotbed but an area of high interest," said Oliver "Buck" Revell, a terrorism expert who was special agent in charge of the Dallas FBI office after the 1993 bombing of the World Trade Center. "The recent flurry of activities that you’ve seen are just the tip of the icebergs."

Two groups - Islamic extremists and hard-line anti-government militias - are drawing the most concern from law enforcement experts as the source of a possible terrorist attack. Both have unique ties to the North Texas region.