The FBI special agent in charge of the New York Joint Terrorism Task Force told Fox News that 15 years after an unsolved bombing of a military recruitment office station in Times Square, he is "definitely concerned" whoever is responsible "could do something like this again."
Robert Kissane issued the warning as the FBI has increased its reward to up to $250,000 for information leading to the arrest and conviction of the suspect or suspects behind the New York City blast.
"We're definitely concerned that they could do something like this again," Kissane said in an interview, adding that "no one should be able should be allowed to get away with setting off an improvised explosive device in New York City, let alone in the center of Times Square. "
The blast in the early morning hours of March 6, 2008, in which a suspect was seen on surveillance footage riding a bicycle before detonating a device that the FBI says was "built using an ammunition can similar to those found on the battlefields in Iraq and Afghanistan," left no one injured.
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However, federal investigators say the "device could have caused significant injury and casualties if people had been close to the blast" and those behind the incident may be linked to two other unsolved bombings in New York City at the British Consulate in 2005 and Mexican Consulate in 2007.
"We have several persons of interest that we've been looking at over the course of the 15 years, but we just don't have enough evidence at this point to make an arrest," Kissane said.
He noted that FBI investigators have gathered a "certain amount of forensic evidence in the case," but that "we don't know who that evidence belongs to."
When asked about a potential motive, Kissane referenced the British and Mexican Consulate bombings in the lead-up to the Times Square detonation and said the theory is that it is "anti-authority, anti-government."
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Kissane says the FBI is hoping that the increased reward will prompt someone to come forward and provide investigators with a break in the case.
"You know, over the course of 15 years, an individual might have had a change of heart in terms of, you know, where they were in 2008 and where they are now in their life and has a better understanding that setting off an IED in Manhattan was an awful thing to do," he said.
"Additionally, you could have a situation where somebody that knew an individual that was responsible for the attack has had a falling out with that individual or those group of people, and they might have the motivation to provide information on that attack and to receive the money," he added.
Kissane also said based on video taken from people in the area and other information investigators have, the FBI believes there might have been individuals conducting surveillance for the mystery bicyclist sought in the Times Square bombing.
"I'm an optimist," he said. "You know, I think ultimately, you know, not in every case, but I think ultimately we tend to get our guy or gal."
Fox News' Tamara Gitt contributed to this report.