As federal law enforcement officials begin to release limited details of their investigation of Farooque Ahmed, the man accused with plotting to set off explosives in several Virginia Metro stations, the subway system is preparing for a busy weekend where two political rallies and the Marine Corps Marathon will bring tens of thousands of new riders.

Some of those riders will likely be nervous about taking the subway ride because of the plot to attack the system.

Metro says riders are a key to system safety.

"It's actually a combined effort. We, ourselves, have a responsibility for maintaining the system in terms of having our transit police out there, but we also rely on our customers. If you see something, say something," said Metro Spokesman Steven Taubenkibel.

Metro is an inviting target for terrorists.

"If you want to paralyze a city or kill a lot of people, a major public transportation system is where you would go," said Ray Locker, the Director of The Investigative Project of Terrorism.

"Can it be adequately protected?" asked 9NEWS NOW.

"You can never stop everything from happening," Locker said.

Metro has 240 uniformed officers who perform random patrols of Metro's 86 stations every hour of every day, the system says.

Although it has a mechanism in place to establish a routine of random bag checks to look for terrorist tools, Taubenkible says that is not under discussion at the moment.

"We've heard from federal law enforcement officials that they believe there is a greater potential for attacks now. They're picking up increasing chatter...so more could be on the way and there could be more arrests," said Locker of the Investigative Project on Terrorism.