An Irishman linked to a criminal clan pleaded guilty today to charges he used forged documents to sell horns from endangered black rhinos to a New York collector for more than £30,000.

Michael Slattery wept, rubbed his face and waved his arms before entering the plea in federal court in Manhattan, prompting US District Judge John Gleeson to comment: "You look like a nervous wreck."

Slattery, 23, told the judge he barely knows how to read but understood the trafficking charges.

"I knew I was doing wrong," he said.

Asked later by the judge how he was doing in jail, Slattery claimed that one inmate had threatened to "spin my head off," and that he'd overheard conversations about how a murder suspect "wanted me to sleep with him."

Prosecutors have identified Slattery as a member of Ireland's gypsy minority. They cited a letter from Irish authorities linking him to an Irish gypsy criminal network based in the County Limerick village of Rathkeale that's suspected in dozens of thefts of rhino horns across Europe.

In Rathkeale, the travellers have purchased "most of the real estate in this town in recent years and shown incredible signs of wealth," the letter said.

According to Europol, thieves known as the Rathkeale Rovers have targeted museums, galleries, zoos, auction houses, antique dealers and private collections in Britain, continental Europe, the United States and South America. It says they were behind a heist this year by masked men who stole stuffed rhinoceros heads containing eight valuable horns from the warehouse of Ireland's National Museum.

US authorities alleged Slattery travelled from London to Houston in 2010 to try to buy two horns at a taxidermy auction house. Learning that he needed to be a resident of Texas to make the purchase, he recruited a day labourer to be a straw buyer. He and other unidentified suspects gave the straw buyer more than £11,000 in 100 dollar bills to complete the deal, a complaint said.

Later that year, Slattery met with a Chinese buyer in Queens and sold four horns using endangered-species bills of sale with fake Fish and Wildlife Service logos on them, the complaint said. It's unclear where he got the additional two horns, it said.

Slattery was arrested in September at New Jersey's Newark Liberty Airport while boarding a flight to London. He faces a maximum term of about 30 months at sentencing early next year, followed by deportation.

In 2011, two Irish nationals from Rathkeale were sentenced to six months behind bars on charges they bought black rhino horns in a sting operation in Colorado. Irish authorities say one of the men is Slattery's cousin.

PA Media