Times Square bomber Faisal Shahzad used inferior explosives to avoid detection, New York’s police commissioner said Tuesday, helping to explain why an international bomb plot ended up a dud.

Commissioner Ray Kelly, speaking to the Center for National Policy, a Washington think tank, discussed his department’s concerns about the changing threats of terrorism. Much of the discussion centered on the case of Mr. Shahzad, a U.S. citizen from Pakistan who left a crudely made homemade bomb smoking in an SUV in Times Square in May. Mr. Shahzad was captured as he tried to flee the U.S. two days later and has been cooperating with authorities, giving them insight into his training by the Pakistan Taliban.

A key question in the early stages of the investigation had been how a trained terrorist could craft such a poorly made bomb, consisting of weak fireworks, propane tanks and nonexplosive fertilizer.

“He tried to lessen the explosive nature of the fertilizer that was used because he thought he would get a higher profile as he went to buy it,” Mr. Kelly told reporters, adding that Mr. Shahzad “sort of dumbed that down.”

Mr. Shahzad also used M-88 fireworks that were much weaker than other alternatives, Mr. Kelly said.

Law enforcement agencies, particularly the Federal Bureau of Investigation, maintain a number of “tripwires” designed to encourage people who sell everyday products that could be used to make explosives to notify agents of any suspicious behavior or purchases. Mr. Shahzad was apparently so worried about the tripwires that he deliberately built a weaker, less effective bomb.

The New York Post reported earlier that investigators had detonated a bomb constructed according to Mr. Shahzad’s original planned ingredients, and found that it would have been deadly. (The Post is published by News Corp., which also publishes The Wall Street Journal.)

While Mr. Shahzad’s decision to buy weaker components marks a kind of victory for counterterrorism authorities, the case also highlights how difficult it is to find terror suspects in the U.S. The police commissioner repeatedly underscored how Mr. Shahzad hadn’t come to the attention of any counterterrorism investigators before the Times Square attempt.

“Shahzad is particularly of concern, that type of individual. He is striving to be middle-class, he becomes a U.S. citizen,” Mr. Kelly said.

“If you look back, he did some radical things, said some very radical things,” he said. “But nobody was looking at Shahzad.”

(Source: WSJ)