Officer Gilberto Valle, as seen on a Facebook page. Valle is accused on plotting to kill and eat women in New York City.Facebook

The cannibal cop case of Officer Gilberto Valle continues to dredge up gruesome details of what prosecutors allege was the 28-year-old’s plan to abduct and eat women. The defense’s response? It was pure fantasy.

While the details are disturbing, so too is the idea of “thought police." Where, exactly, does U.S. law draw the line between fantasy (no matter how dark) and conspiracy?

“In this country, it is a crime to conspire to commit a crime,” said Joe DeMarco, an Internet lawyer and former head of the cyber crimes unit at the U.S. Attorney’s Office in New York. “So, if we agreed to buy a kilo of cocaine and break it up into little bags and sell it, even if we never did it, it’s a conspiracy that violates the narcotics laws of the U.S., and we could go to jail for years and years...We like to stop a crime before it happens.”

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But, criminal law doesn’t go after fantasies, said Marcus Asner, partner at Arnold and Porter, a New York law firm, and former chief of the major crimes unit at the U.S. Attorney’s Office in Manhattan. Criminal law separates between actus reus and mens rea, Latin terms meaning guilty act and guilty mind, allowing some leeway in guilty thoughts -- meaning that almost all defendants argue they were simply pretending.

“Suppose you’re at a target range and you don’t realize someone is behind the target, you pull the trigger and someone accidentally gets killed. In that case, you’re not guilty,” Asner said. “It was an accident. On the other hand, if you are shooting at something thinking it is a person, and you intend to kill a person, but in fact the person is not there and no one gets killed, there is no completed crime -- but we call that attempt and attempt is a crime.”

In reality, though, it’s blurry, he said. One key question that often helps define cases is whether the defendant took a substantial step toward the crime.

Take a case he argued in 2005, U.S. vs. Joseph Zito. Zito often got online to look for young girls, and eventually, he started chatting with an FBI agent he believed to be a young girl.

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“The government figures out who he is but doesn’t arrest him until he gets in the car and shows up to meet the girl with sex paraphernalia in the trunk of his car,” Asner said. “We were very careful to make sure the guy did take a substantial step.”

One of the arguments against Valle is the specificity he used in his communication.

“This is someone who hasn’t just idly talked about cannibalism, but he’s named specific people,” DeMarco said.

Further complicating the “I was just pretending” defense is the Internet.

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“The Internet allows people who have these niche interests to find each other in ways that are efficient, global, and, if you want, anonymous,” DeMarco said. “It enables people with disparate interests -- whether it be stamp collecting or cannibalism -- to find each other. And that can validate their interest, so they don’t feel alone or odd or unusual.”

That validation can lead to encouragement, DeMarco said, so that someone who was initially only mildly interested in stamp collecting, for example, could form a club. And when the subject is something society disapproves of, it can encourage someone to cross certain lines they might not have otherwise.

“The very probing question is, What is the difference between fantasy and what’s blameworthy?” Asner said. “At bottom, it’s a moral judgment. Oftentimes, that is for the jury to figure out.”