Video: FBI issues new terrorism warnings

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    >>> permit for the tent. now, to the alleged terrorist plot we have been reporting on for days, apparently directed at targets here in new york city . tonight, police and fbi agents are trying to unravel what they have here. in the meantime, the feds issued new advisories for sports venues and hotels across the country. our justice correspondent, pete williams with the latest on this. good evening.

    >> reporter: the fact the homeland security advisories are so jeng is a clear sign investigators don't know what the actual target was. because investigators believe a target of the plot might have been mass transit , security was more visible on big city trains and subways including the commuter lines. homeland security urged individual lens in sports arenas and entertainment complexes. there were no known plots against such sights. they did not change security in response to the bulletin.

    >> they think -- as i say, we are every day up to a level that i think.

    >> reporter: in new york and denver, scores of police and federal agents checked companies that sell the materials listed on the laptop of janlg beulah zazi to see if they bought the supplies.

    >> they were inquiring if individuals of companies were purchasing large quanties of chemicals.

    >> reporter: similar questions at storage facilities. so far, nothing shod up. zazi filed for bankruptcy, more than $50,000 in debt. he's tried to mislead them saying a possible attack target might be a big discount store outside new york. they say, there's no reason to think it's true. trying to identify who was involved remains urgent priority. anyone in contact with zazi , more arrests are coming.

    >> pete williams , thanks. we turn

updated 9/22/2009 9:34:06 PM ET 2009-09-23T01:34:06

A quart-sized container of homemade explosives is cheap, deadly and difficult to detect — and that is exactly why the type of chemical bomb feared to be at the heart of a terrorism investigation worries law enforcement so much.

As FBI and New York police counterterrorism agents investigate a Denver man who authorities say received al-Qaida explosives training and recently traveled to New York, law enforcement officials around the nation have been advised to be on the lookout for any signs of bombs built with hydrogen peroxide.

That type of weapon killed 52 people in the London transit system four years ago. During the morning rush hour of July 7, 2005, three men carried backpacks that exploded within 50 seconds of each other on three London Underground trains. A fourth bomb exploded on a bus nearly an hour later.

The same chemical components were allegedly at the heart of a failed plot to blow up commercial passenger jets leaving England for America. That plot was based, according to court evidence, on amounts of chemicals small enough to fit into soda or water bottles.

Plot to detonate similar devices?
Now, according to law enforcement officials speaking on condition of anonymity because they were not authorized to discuss the investigation, authorities are concerned that 24-year-old Afghan immigrant Najibullah Zazi may have been trying to put together a plot to detonate similar devices in backpacks, possibly on crowded commuter trains in New York. Zazi has been charged only with lying to authorities, and has told reporters he has nothing to do with terrorism.

Dan Watts, a research professor at the New Jersey Institute of Technology, said a bomb made from hydrogen peroxide is very different from the kind of truck bomb explosion used in the 1995 attack on the federal building in Oklahoma City.

"With a hydrogen peroxide-based explosion, you won't get that kind of damage. They're more effective in a more confined space. When you hear about them being particularly horrific, it's a railroad car, a situation like London, rather than trying to bring down a big building," said Watts.

When mixed together to make a bomb, the material is so unstable, it can be triggered accidentally by heat or shock.

In a laboratory setting, a quart of the material exploding can destroy the entire lab, said Watts.

"They don't blow the walls down, but everything in the lab can be ruined," he said.

Signs of possible bomb-making
Shortly after federal agents looking for explosives raided several Queens apartments linked to Zazi, officials in Washington issued a bulletin to police around the nation specifically citing the case and urging them to be on the lookout for any signs of people building peroxide-based bombs.

Such signs include burn marks on people who have handled the bomb components, apartments using large fans or big refrigeration units, and purchases of large amounts of certain household chemicals to make the bombs.

That Sept. 14 bulletin also reminded police that recipes for building bombs are taught in terrorist training camps and in widely circulated terrorism manuals.

"Hydrogen-peroxide based explosives are powerful and highly unstable; furthermore, similarities in appearance and methods of production can cause first responders to mistake certain explosives for chemicals used to manufacture narcotics," the bulletin says, reminding officers of the London attacks and telling them such bombs can be carried in "a backpack, suitcase plastic container, or other hand-carried item."

Copyright 2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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