NEW YORK -- A police officer on trial for conspiracy to commit cannibalism considered the woman who was his New York Police department supervisor as a potential target of kidnap and torture, an FBI agent testified Thursday.

The testimony came amid a report that a man considered to be one of Officer Gilberto Valle's co-conspirators, identified in the U.S. case by the online name Moody Blues, had been detained but released in a separate case in Great Britain.

Returning to the witness stand at Valle's federal trial in Manhattan, FBI agent Corey Walsh told jurors that a search of Valle's computer had turned up a file with multiple photos of a woman the agent identified as an NYPD officer who supervised Valle. The government had previously introduced a transcript of a February 2012 email exchange in which Valle offered a co-conspirator a menu of women he could abduct for rape and torture.

"The second girl listed is a cop - Evelyn, 33 years old," Valle wrote.

"No I want a reg girl," the man responded.

The revelation came as the defence sought to discredit allegations that the 28-year-old Valle conspired with Internet friends to kidnap, kill and eat women, pressing Walsh on why some communications were deemed proof of a crime while others were deemed fantasies.

Defence attorney Robert Baum directed Walsh to obvious falsehoods in communications that the government has used as evidence Valle was a threat. In one, Moody Blues insisted he and Valle would need a secluded place to cook a woman alive.

"I have a place on the mountains," Valle wrote. "Nobody's around for three quarters of a mile."

Asked if that was true, Walsh testified that authorities "are not aware of a place he had in the mountains."

Valle has been held without bail since October, when he was arrested on charges of conspiring to kidnap women in a cannibalism plot born on the Internet. Throughout the trial, which began Monday, Valle's lawyers have attacked government evidence as nothing more than the reflection of a man engaging in extreme sexual fantasies with like-minded people around the world. The government has conceded that Valle never met the purported Internet co-conspirators and no women were harmed.

Jurors have heard testimony from Valle's estranged wife and from former classmates and other women who testified they knew Valle on a casual basis and never considered him dangerous. Their testimony was followed by evidence that all of them were the subjects of emails and chats describing how they could be snatched away and eaten.

One of the women, special education teacher Alisa Friscia, appeared angry and agitated as she testified on Thursday that she had worked with Valle's wife but wasn't close to her.

As for Valle, she snapped: "No, he's never been a friend!"

She was followed to the stand by police Officer Robin Martinez, a police academy instructor, who said there were severe penalties for unauthorized searches of the national police database that Valle was accused of abusing to collect information about targeted women.

"You are going to face serious trouble, including being prosecuted, being arrested, being fired," she said.

Prosecutors allege Valle's cyber co-conspirator Moody Blues told the officer he had killed and eaten at least two women. The New York Post reported Thursday that two men had been arrested in a child porn case in Britain and that one was Moody Blues.

When asked Thursday whether there had been any arrests related to the Valle prosecution in New York, local police in the southern England county of Kent said they had briefly detained two men from the area around Canterbury, the famous cathedral city about 60 miles (96 kilometres) southeast of London.

Kent police identified the men only as a 57-year-old and a 30-year-old, saying that they had been arrested a week ago on suspicion of conspiracy, child grooming and possession of child abuse images.

No charges had been filed, and police said the men have since been released on bail.

The statement said Kent police had "been in contact with U.S. law enforcement agencies in relation to this investigation" but did not go into any further detail.

An FBI spokesman in New York declined to comment.