he powerful blasts at the Boston Marathon finish line Monday underscore why the Federal Bureau of Investigation has spent years refining its “tripwire” system for catching would-be bomb makers before they can build a deadly device.
For years, federal agents have asked businesses that sell materials useful in making bombs to alert authorities to any suspicious orders. The types of tripwires in place have shifted over the years. In the 1990s, law enforcement worried mostly about fertilizer-based bombs after such devices were used in the Oklahoma City attacks of April 1995. In the past decade, chemical-based bombs have come into focus as authorities adapt to the changing threat.
“The tripwires have certainly been successful in the past,” said Don Borelli, a former counterterrorism official at the FBI who now works for Soufan Group.
He pointed to the case of a Saudi man, Khalid Ali-M Aldawsari, who was convicted last year of attempting to use a weapon of mass destruction. That case began in February 2011 with a tip from a North Carolina chemical-supply company about a suspicious $435 order by Mr. Aldawsari, who was legally in the U.S. on a student visa. A shipping company separately notified authorities the same day that it had similar suspicions because the order didn’t appear intended for commercial use.
In a matter of weeks, agents had secretly searched the suspect’s apartment, as well as his computer and email. The FBI found a journal entry by Mr. Aldawsari in which he wrote that he had been planning a terror attack in the U.S. for years. Authorities say that he was trying to make a chemical explosive similar to TNT. FBI experts said the amounts that were used in the Aldawsari case would have yielded nearly 15 pounds of explosives. He was convicted in June 2012.
The tripwire program can work even when suspects don’t buy the materials that counterterrorism officials worry about. When Faisal Shahzad tried to detonate a car bomb in Times Square in May 2010, he intentionally worked with less-powerful substances. He was worried that if he bought materials to carry out the recipe of his Pakistani-based handlers, store owners would alert the FBI, according to statements he later made to investigators.
Investigators haven’t said yet what explosives were used in Monday’s attack in Boston, so it is unclear if any purchases could have been picked up by the FBI’s tripwire efforts.
The tripwires aren’t always successful. In a 2009 plot to bomb the New York City subway system, suspect Najibullah Zazi was able to purchase significant quantities of hydrogen peroxide, which he hoped to distill to a higher concentration that would make an effective bomb. Law-enforcement sources say Mr. Zazi’s plot wasn’t uncovered by the tripwire system, but through international intelligence-gathering. He eventually pleaded guilty to plotting with others to bomb the subway system.
Bomb plots, successful or not, typically prompt counterterrorism officials to review the tripwire system and look for possible improvements, a process just beginning in the Boston investigation.
After the explosions near the marathon finish line, counterterrorism officials scrambled to inspect a large number of discarded bags in and around Boston. They found some additional suspicious items and were investigating Monday evening whether they were bombs, according to people briefed on the matter. A law-enforcement official said late Monday that investigators initially believed some devices could be bombs, but closer examination led them to doubt that was the case.
The suspicious items were discovered over the course of a frantic inspection of packages, many of them abandoned as pedestrians, runners and others rushed away from crowded public streets.
The head of the Boston FBI office, Richard DesLauriers, said the agency’s joint terrorism task force would take the lead on the investigation, and federal agents were already traveling to the area. He asked for the public’s help to generate tips and leads in the case.
Any unexploded devices would be valuable evidence for investigators to determine who was behind the bombing. Even without unexploded devices, investigators can still sift through the blast marks of the detonated devices to determine how the bombs were constructed.
Other Major Plots in the U.S.
Feb. 26, 1993: Six people die when terrorists blow up a truck bomb under one of the World Trade Center towers. Ramzi Yousef is later convicted of masterminding the attack and is serving a life sentence.
April 19, 1995: Bomb destroys Alfred P. Murrah Federal Building in Oklahoma City, killing 168 people. Timothy McVeigh and Terry Nichols are found guilty of the attacks. McVeigh is executed in June 2001, and Nichols is serving a life sentence.
July 27, 1996: Bombs at Centennial Olympic Park during the 1996 Atlanta Games kill one woman and injure about 100 others. Eric Rudolph pleads guilty to setting off the bombs and is sentenced to life in prison.
Dec. 14, 1999: ‘Millennium bomber’ Ahmed Ressam is arrested crossing the Canadian-U.S. border. He is later convicted of a plot to bomb Los Angeles International Airport on New Year’s Eve 1999 and ultimately sentenced to 37 years in prison.
Sept. 11, 2001: Terrorists hijack four planes, destroy the World Trade Center in New York and hit the Pentagon. Nearly 3,000 people are killed. Khalid Sheikh Mohammed and four others face charges connected to the attacks at Guantanamo military tribunal.
Fall 2001: Mailings containing anthrax kill five people and sicken 17 others. U.S. authorities later conclude that government scientist Bruce Ivins, who committed suicide in 2008, was the culprit. Ivins’s defenders question the conclusion.
Dec. 22, 2001: ‘Shoe bomber’ Richard Reid tries to blow up a flight from Paris to Miami by igniting explosives hidden in his shoe. The attempt fails. He pleads guilty and is sentenced to life in prison.
September 2009: Najibullah Zazi drives to New York City with plans to attack subways after concocting homemade bombs. He is caught before the plot can be carried out. He and others are convicted on federal terrorism charges.
Dec. 25, 2009: ‘Underwear bomber’ Umar Farouk Abdulmutallab attempts to set off bomb on plane approaching Detroit from Amsterdam, but crew members and passengers extinguish it. He is sentenced to life in prison.
May 1, 2010: Faisal Shahzad leaves vehicle near Times Square in New York City with crude bomb inside. His attempts to ignite the bomb fail. He pleads guilty and is sentenced to life in prison.
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