The elaborate sting operation that led to the arrest of a Bangladeshi man accused of plotting to blow up the Federal Reserve Bank of New York was a "picture-perfect" example of how such undercover operations can thwart potential terrorist attacks, law enforcement experts said Thursday.

Such stings have sometimes raised complaints from defense lawyers of entrapment, but law enforcement regards the tactic as valid and essential in fighting terror.

"They do these things because they are attempting to head off some possible violence by way of an attack," said James Cohen, an associate professor at Fordham University School of Law.

But "it's a significant risk, at least in theory, that they are really turning people who are what we might consider to be acting out politically -- espousing anti-U.S. dogma -- who never would have picked up anything [to carry out an attack] into people who do," he said.

Cohen and other experts said the case of Quazi Mohammad Rezwanul Ahsan Nafis, who was arrested Wednesday, appeared to be an example of law enforcement acting astutely and within the law to head off a potential plot.

"It's a picture-perfect example they should use in training agents," said Joseph King, an associate professor at John Jay College of Criminal Justice in Manhattan and a former head of the National Security Section in New York for the U.S. Department of Homeland Security.

"You do it because it's proactive," he said. "You can't just be reactive. Do you want to try to intercept these things or do you want to try and wait and respond to the bombing and then clean it up?"

One caution, experts said, is that if law enforcement pushes or leads a suspect into trying to carry out a terrorist attack, their defense lawyers will argue in court it was entrapment.

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In a 2011 trial of several men accused of planting bombs in front of a Riverdale synagogue, they argued that they did it because of persistent urging from an informant, and even the judge said that "the government made them terrorists." Their convictions are on appeal.

"The line is, who is creating the criminal scheme," said Sam Braverman, one of the defense lawyers in that case. "If the individual is the one who is predisposed [to a crime], then the individual should be arrested and convicted. But if the government [agents or informants] holds out the carrot of money or fame and then convinces the person to commit the crime, then the government is committing the crime."

As the Nafis case unfolds, Braverman said, "we should all ask ourselves if this is what it appears to be."

Police Commissioner Ray Kelly told reporters Thursday that entrapment "has "been raised many times in cases like this and it has not prevailed."