The number of names on an FBI-maintained list of suspected terrorists has risen by nearly 500 percent over four years, leading members and witnesses at a Senate Homeland Security and Governmental Affairs Committee hearing to question the standards used to nominate people for inclusion.

“With the list likely to go over a million names in the near future,” said Chairman Joseph I. Lieberman, I-Conn., “we need to know that there are clear standards for placing names on it.”

The FBI-operated Terrorist Screening Center uses a “reasonable suspicion standard” to determine if people should be included on the lists. Generally, a government agency will first deem that someone is “reasonably suspected” of planning a terrorist attack or associating with terrorists, then send the information to the National Counterterrorism Center for a separate determination. If the National Counterterrorism Center also decides the person is suspicious, the information is sent to the Terrorist Screening Center for a final decision and, possibly, addition on one of two master lists.

The center was created in December 2003 to consolidate all the different terrorist watch lists maintained by various federal agencies into one master list, which would be used across the government. The center succeeded — almost. It weaved the numerous agency watch lists into two master lists.

However, the center needs to do more fine tuning to make the lists more useful, eliminate duplicative names, redress misidentified individuals and pare down a growing inventory, according to witnesses at the hearing on Wednesday.

Justice Department Inspector General Glenn A. Fine said the Terrorist Screening Center could start by consolidating the two master lists into a single inventory.

Leonard Boyle, director of the center, said there is one system maintained for ingesting new watch list data and another for exporting data to other agencies, such as the Transportation Security Administration and U.S. Customs and Border Protection and other federal stakeholders.

According to Fine, the center should also focus on:

• Performing quality assurance procedures on the database and regularly reviewing them.

• Developing a policy to reduce the number of people on the lists.

• Providing more timely redress for misidentified people.

• Ensuring watch lists always get sent to other agencies’ databases.

The Terrorist Screening Center should also consider providing the entire master list to stakeholders, said Eileen Larence, an auditor at the Government Accountability Office.

Screening agencies, which both provide information to the Terrorist Screening Center and receive it back, generally don’t check against all records on the consolidated watch lists. That’s because it isn’t needed to meet their mission or the agency’s computer programs prohibit it. U.S. Customs and Border Protection’s receives the highest percentage of names from the master lists and the Transportation Security Administration receives fewer because its system won’t accept incomplete identity data, she added.

This story originally appeared in CQ Homeland Security.