WORCESTER — In a case that could raise the depravity bar to new heights, Worcester resident Geoffrey R. Portway accepted a federal plea deal Monday after admitting to possessing and distributing child pornography and scheming to abduct, kill and eat children.

Portway, 40, a British citizen, engaged in numerous online chats with multiple individuals about "a mutual interest in abducting, raping, murdering and eating children," according to the terms of a plea deal that will net the Worcester man 18 to 27 years in federal prison. He also must register as a Level 3 sex offender, placing him in the category for sexual predators deemed most likely to commit similar crimes again, and submit to lifelong supervision after serving his term.

"Clearly, the facts of this case were quite disturbing and we are grateful law enforcement acted when they did," U.S. Attorney Carmen M. Ortiz said. "I hope that this case sends a clear message that we will prosecute to the fullest extent of the law those who participate in these types of activities."

Though some criminals attempt to shield themselves with the anonymity of the Internet, "the Department of Justice is committed to aggressively pursuing them to ensure that there is no place to hide," Ortiz said.

The probe, dubbed Operation Holitna, began in Milford in 2010 and quickly expanded to Europe and beyond, according to federal officials. "Since we began this operation ... a worldwide network of offenders has been, and continues to be, unraveled, including Portway," said Bruce M. Foucart, special agent in charge of Homeland Security Investigations in New England.

The investigation kicked into high gear after the arrest of Milford resident Robert DiDuca, who last year was sentenced to 18 years in federal prison for his role in the case. Since then, law enforcement officials have pieced together a worldwide web of digital depravity, leading to 51 suspects and saving some 160 children from harm, according to Foucart.

Federal officials said many of Portway's online conversations were accompanied by the trading of child porn. Investigators said these chats included images of kids known to suspects and detailed desires to sexually abuse, murder and cannibalize them.

Portway mainly solicited help from Kansas resident Michael Arnett, also charged in connection with the case. Portway and Arnett discussed abducting children to use in rape and torture scenarios, according to investigators. Portway used Skype and other programs to communicate with Arnett and to trade child pornography and images of injured, mutilated and deceased children, federal prosecutors said.

Since roughly 2010, Portway repeatedly solicited Arnett to kidnap a child for him, with the intent that Portway would ultimately rape, kill and eat that child, prosecutors said. The discussions involved real children who were identified by name in photographs, officials said.

On July 27, 2012, local, state and federal law enforcement officials executed a search warrant at Portway's Worcester home on Beechmont Street, where authorities said they found a dungeon containing a child-size homemade coffin, a steel cage, torture devices and butchering tools. Law enforcement officials said they also seized various computers and digital devices containing Portway’s child pornography collection, as well as the computer he used to communicate his plans with others.

To reach the basement dungeon, one had to unlock a door that entered a sally port leading to another locked door. Behind that door, officials said, was a lair lined with "acoustical sound-deadening material" that contained a chair and television and apparent Internet cable access.

Authorities said both the coffin and steel cage had exterior locking devices. The room contained a steel tabletop with steel rings at six points, presumably for restraining victims, officials said. Authorities said they also found a cabinet freezer, an upright freezer, disposable scalpels, butchering kits and castration tools.

Recovered online chats revealed Portony intended to use the dungeon as a place to confine kidnapped children prior to raping, murdering and eating them, according to investigators.

Portway is scheduled to be sentenced Aug. 2 in U.S. District Court in Worcester. He will deported after serving his prison sentence, according to the plea agreement. Federal prosecutors are asking anyone with additional information to call Ortiz's office at (617) 748-3274.