"We're very careful in telling sources what to say and what not to say because, obviously, you can provide the opportunity, but you don't want to push it too far," former FBI special agent Brad Garrett said.
In this most recent case in Riverdale , we saw something we don't always see.
The FBI's undercover operation involved far more than surveillance.
Authorities ultimately used inert explosives and an inactive missile just to prove their case.
Randy Mastro, a former deputy mayor who helped establish the city's Office of Emergency Management, said there's a reason authorities took things further this time.
"This incident proves once again that terrorism is a hate crime and, as a result of this investigation, we're able to identify at least this band of terrorists, who and what would be potential targets," Mastro said.
Infiltration worked very well in Fort Dix two years ago. A group of would-be terrorists were undone after authorities used two paid informants.
In Miami, prosecutors ultimately got convictions the same way, but it was only after years of mistrials in which defense attorneys argued entrapment and so, experts say, the key really is control.
"The concern always is are these people or are the sources connected to anyone else, because then are there side conversations? Are there other things going on?" explained Garrett.
In this case, authorities also asked the question just how great is the risk?
"They wanted to kill people. They wanted to do significant damage. They made virulent anti-semitic statements. They clearly wanted to cause significant damage," NYPD Commissioner Ray Kelly said.
This sting operation was led by an FBI informant who, instead of going to prison for fraud, agreed to go undercover.
Investigators said the group that he targeted became Islamic converts in prison, which raises the question whether prison is a breeding ground?
Earlier this year, California inmate Kevin James was convicted on terrorism charges for converting fellow inmates to radical Islam and plotting to bomb military installations and synagogues. He joins a long list of terrorists to come out of prisons, including Jose Padilla of dirty bomb notoriety and the convicted shoe bomber Richard Reid.
"Prisons have been breeding grounds for radical thoughts and views for centuries," said Frank Cilluffo of the Homeland Security Policy Institute.
It's still unclear whether those accused in the plot to blow up two synagogues in the Bronx were radicalized in prison, but it appears that's where they converted to Islam. The threat of homegrown terrorism taking root in our prisons has been a concern of the NYPD for sometime. Their own report states prisons provide "extremist fodder and fuel for radicalizing."
"You have a captive audience, you have a group more susceptible to extremists views and those who can manipulate that environment can do an awful lot," Cilluffo said.
In a report from the Department of Justice, the FBI expressed concern that "inmates were logical targets for terrorists recruitments" further claiming they often left prison "with extreme Islamists views." Experts say that about 18-percent of New York's 64-thousand inmates are Muslim, the vast majority peaceful and no more a threat than Christian or Jewish prisoners.
"I'm more concerned about a charismatic leader who can distort a religion and sadly when dealing with terrorism the numbers don't have to be high," said Cilluffo.
The threat is nearly impossible to measure. All the more reason for law enforcement to keep a watch behind bars.
"There's a potential for radicalism to take place anywhere, more so in prisons, but I do believe law enforcement is aware and keeping a careful eye," Senator Charles Schumer said.
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