NEW MILFORD - A New Milford man whose co-worker made up a story that he was planning terrorism is facing deportation to Mexico, according to local police, while his co-worker is being charged with filing a false report.

Police say that Sixto Guerra, of Danbury, disliked Garzon Contreras, who worked with him at a New Milford diner, so he sent a letter to police alleging that Contreras was “plotting with ISIS” to attack the Elephant’s Trunk Flea Market in New Milford, the Seymour Public Library and the village of Sandy Hook.

“Please prevent this bloody massacre,” the letter stated, according to police. “We don’t want more innocents to pay for this anger.”

The letter also claimed that Contreras and ISIS members had previously planned an attack at the Dutchess County Fair but that their equipment wasn’t available in time. He said Contreras was in possession of an AK-47, grenades and homemade explosive devices.

None of this was true, but in the course of investigating, police determined that Contreras was an undocumented immigrant. They contacted the Department of Homeland Security and Immigrant Services, whose agents arrested Contreras. He was previously deported to Mexico in 2011 and 2012, but returned to the United States.

Investigators had contacted Elephant’s Trunk shortly after receiving the letter about canceling that weekend’s event. Organizers said it would cost them more than $45,000 to do so, and instead requested additional police presence at the flea market.

Investigators, who were working on conjunction with state and federal officials on the case, interviewed Contreras’ landlord as well as his employer, who both said he was a “hard worker” and not a threat to anyone.

Contreras, when contacted by police, agreed to let police search his home, and nothing was uncovered. He told police that he had no idea who would try to get him into trouble with the exception of his co-worker, Guerra. They worked together at the Dinerluxe on Danbury Road.

While Guerra initially denied sending the letter to police, forensic evidence connected him to the document.

Authorities continue to search for Guerra, who faces a charge of falsely reporting an incident.