As authorities in New York touted their success in foiling an alleged terror plot, new questions were raised about the seriousness of the threat, with reports that the FBI declined to investigate the suspect because it did not consider him an effective terrorist.
Mayor Michael Bloomberg said the arrest of Jose Pimentel, 27, marked the 14th time that a conspiracy aimed at harming New Yorkers had been thwarted since the 9/11 attacks of 2001.
He and the police chief, Raymond Kelly, described Mr Pimentel as a "lone wolf", who was driven by his sympathies with al-Qa'ida to plot to attack targets. They said he had been assembling a pipe bomb when he was taken into custody. He appeared in court accused of plotting to blow up police and US troops returning home from Iraq and Afghanistan.
Sources at the FBI, however, suggested the agency had twice declined to assist in the investigation because it hardly considered him a serious threat, owing to his emotional and mental problems. "He didn't have the predisposition or the ability to do anything on his own," one FBI source told the Associated Press.
Mr Pimentel, a US citizen born in the Dominican Republic, was was known as Muhammad Yusuf and had a website, trueislam1.com, on which he praised jihad and criticised the US overseas policy.
"People have to understand that America and its allies are all legitimate targets in warfare," he wrote online last May. Pimentel smiled as he was ordered to be held without bail until his next court appearance on Friday.