http://abcnews.go.com/sections/WNT/I..._040405-1.html

British authorities believe terror suspects arrested last week were planning to make a bomb that would include a highly toxic, easily obtained chemical called osmium tetroxide, ABCNEWS has learned.

Used primarily in laboratories for research, osmium tetroxide is known to attack soft human tissue and could blind or kill anyone who breathed its fumes. According to the New Jersey Department of Health, it is a colorless to pale yellow solid with a strong, unpleasant odor.

"It's a nasty piece of work," said Dave Siegrist, a bioterrorism expert at the Potomac Institute for Policy Studies in Arlington, Va. "It irritates the eyes, lungs, nose and throat. It leads to an asthma-like death, what we call a 'dry-land drowning.' "

Scientists say if, for example, the bomb used in the 1993 World Trade Center attack had produced such fumes, they would have wiped out the first police and rescue workers on the scene.

"They become overwhelmed by fumes," said Jerry Hauer, an expert on biological and chemical terrorism and director of public health preparedness at the Department of Health and Human Services, describing what could have happened. "They can go blind. This is not a benign chemical. It is very nasty."

Eight British citizens of Pakistani descent were arrested and taken into custody when 700 police raided 24 locations in and around London on March 30. Investigators say British authorities moved in when they learned from electronic intercepts the dangerous chemical was involved in the plot. They had been the tracking group's activities for several months.

According to sources, there was some indication the group in custody was targeting Gatwick airport, the British public transportation system and enclosed shopping areas. British authorities feared it had the potential to be one of the worst attacks ever against the United Kingdom.

Even though the arrests were made in the United Kingdom, authorities say the operation was being run out of Pakistan by a suspected al Qaeda figure.

"They are creative in their planning," said Hauer. "They continue to work around our systems."