NEW YORK -- A New York City police officer told investigators after his arrest that his online chats about cannibalism set him on a downward spiral that was wrecking his personal life, an FBI agent testified Friday.

Gilberto Valle "claimed he did not enjoy it and he did not know why he was doing it," agent Anthony Foto told jurors at Valle's federal trial in Manhattan.

Foto testified that after his October arrest, Valle acknowledged talking to people about a fetish of kidnapping, killing and eating women wasn't satisfying.

However, he "claimed he would not have gone through with it," the agent added.

The testimony came as the government winds down its case against the 28-year-old officer. Valle contends that it was all fantasy and that he intended no harm.

The trial's first week concluded on Friday afternoon. Jurors were due back on Monday.

The government called agent Foto on Friday to recount the arrest and initial interview of Valle late last year on kidnapping conspiracy charges.

When agents arrived to pick up Valle at his Queens home and told him to stay calm and everything would be fine, Valle responded: "I don't think so," the agent said.

Under interrogation at FBI headquarters, Valle lamented that his chats and emails with others on the Internet about cannibalism were leaving him exhausted and uninterested in sex with his wife.

He never said he harmed anyone, and he offered to help the FBI distinguish between which people on the Internet were real threats and which were not, Foto said.

The agent said that when he asked Valle why he thought he was being arrested, the officer said he believed it was for conspiracy to commit murder or attempted murder. But Foto later conceded that Valle made the remark an hour into an interview that lasted several hours.

On cross-examination, defence attorney Robert Baum drew the jury's attention to moments when the FBI tricked his client, including when the FBI told him he been under investigation for more than a year.

"That was a lie, right? Baum asked.

"Of course," Foto responded, acknowledging that Valle had been under investigation for only a few weeks. He said the ruse was investigative technique aimed at getting the defendant to speak.

After the testimony, U.S. District Judge Paul Gardephe sent the jury home for the day. He spent the afternoon hearing proposed testimony from an FBI expert who studied Valle's computer history, finding numerous gruesome images and some videos.

Defence lawyers are opposing the presentation of as many as 34 ghastly exhibits of images, including women being tortured, dead bodies and body parts.

Gardephe put off a ruling on Friday on whether jurors would see the pictures, which defence lawyers say may have been saved automatically without him ever seeing them when he went on certain websites.

The government says the exhibits include a picture of a dead body with feet unattached, an image Valle's wife testified she saw when she went to one of his favourite sites and discovered why he stayed up late online.

Valle has been held without bail since his October arrest. 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 that 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.