Pamela Hess / AP - Tracking scientists moving from country to country to share their expertise in building biological weapons is a major challenge, a top U.S. intelligence official said Wednesday.

Unlike nuclear weapons or missiles, biological weapons can be manufactured in relatively nondescript facilities that are hard to detect. That makes tracking the people with the know-how to build the weapons themselves even more critical, said Vice Adm.

Robert Murrett, director of the National Geospatial Intelli-gence Agency. The agency analyzes imagery intelligence that comes from aircraft and satellites.

Biological weapons use viruses, bacteria or toxins rather than explosives to target people, animals or agri-culture. They can be loaded onto a traditional warhead or dispersed by less sophisticated methods, like the letters containing deadly anthrax spores mailed to Congress and media outlets in 2001.
Because they are easier to hide than nuclear weapons or missiles, biological weapons are best tracked by monitoring those with expertise to make them - a formidable challenge in itself, Murrett said.

"The kind of challenge we have for proliferation which I think is tougher is, for example, the transfer of individual scientists from country A to country B," he said at a breakfast with defense reporters.

Tracking individuals trying to spread biological weapons know-how is beyond the capabilities of his agency alone, Murrett said. It requires multiple intelligence agencies to combine their intercepts, data bases and analyses. "That's probably working as well today as maybe it ever has," he said.

The NGA's classified annual budget has increased significantly in the past five years, in large part to sup-port the demands of war commanders in Iraq and Afghanistan, he said.

Murrett said he has sent additional people to Iraq to help with U.S. efforts to target insurgents at the neighborhood level and more recently to Afghanistan to focus on the Pakistan border, where al-Qaida has re-established itself.