By Chris Francescani

NEW YORK (Reuters) - Closing arguments were due to begin on Thursday in the federal trial of the "cannibal cop," a New York City police officer accused of plotting to kidnap, cook and eat women.

Officer Gilberto Valle, 28, has pleaded not guilty to a charge of conspiring to kidnap, and said he was merely engaged in online fetish role play. Federal authorities contend he took real-life steps to act on his fantasies.

Valle, dubbed the "cannibal cop" by tabloid media, did not testify. Defense attorneys scrapped a plan to call a psychiatrist to testify that he suffered from a disorder in which he derives sexual pleasure from others' suffering.

SPOTLIGHT ON FETISH WEBSITES

The trial has shined a spotlight into a shadowy region of cyberspace where millions of people trade talk, images and video of extraordinary brutality, most of it apparently staged.

On Tuesday, defense attorneys took jurors on a video tour through DarkFetishNet.com, the website at the heart of the case.

Its creator, Russian web entrepreneur Sergay Merenkov, compared the site to Facebook, and some jurors let slip rare smiles.

The website is structured and functions like mainstream social media networks. But instead of family photos and cat videos, fetish network members share photos and videos of extreme human cruelty, with the goal of sexual stimulation. Scenarios involve asphyxiation, necrophilia, beheading, hanging and rape. One group celebrates "pregnant belly executions."

People even trade virtual gifts, only instead of a clutch of daisies or an e-cupcake, people trade diamond-eyed skulls and miniature instruments of torture.

Merenkov, 34, said in videotaped testimony that his 38,000-member website is tiny compared to more popular sites like FetLife, short for fetish life, which counts more than 2 million members. Seventy percent of DarkFetishNet members are Americans, he testified.

Members dream up brutally violent scripts "like a scenario for a movie - they all have a role to play out," Merenkov said.

FANTASY OR REAL LIFE?

But lurking among millions of webpages full of bondage and sadomasochism enthusiasts is a darker element, Merenkov testified. He said he has kicked members off the site when "let's say that it seemed not to be fantasy anymore."

Prosecutors said Valle revealed himself to be such a person when he began taking steps to act on his fantasies.

Valle reconnected with a former classmate he had discussed kidnapping and torturing online, and took her to brunch "to decide whether to kidnap her," an FBI agent who interviewed Valle after his arrest testified last week.

Another expert said Valle had improperly accessed a law enforcement database to gather personal information about other alleged targets. He is also charged with that crime, which carries a maximum sentence of five years in prison. A conviction on the conspiracy charge carries a sentence of 20 year to life.

Prosecutors have tried to show that Valle's life was unraveling before his arrest.

He was spending more time on fetish sites, despite telling an investigator after his arrest that he didn't like the website, and couldn't explain why he continued to visit it, even on his cellphone while on duty.

Valle was suspended from the department after his arrest.

(Reporting By Chris Francescani; Editing by Alden Bentley)