(CNN) — An Australian businessman pleaded guilty Thursday to strapping a fake bomb around an 18-year-old girl’s neck in an attempt to extort money from her family, a court representative said.

The guilty plea by Paul Douglas Peters at Sydney Central Local Court is the latest development in a case that grabbed the attention of the international news media last summer.

Peters, who is in his 50s, was traced to the United States and arrested in Kentucky, more than 9,000 miles from suburban Sydney where the dramatic events took place in early August. He was extradited back to Australia in September.

The authorities say Peters attempted to extort money from Madeleine Pulver’s family in the suburb of Mosman by fastening a black box around her neck.

In a note, he said the box contained “powerful new technology plastic explosives” that would go off if Pulver did not follow his instructions, according to a complaint for provisional arrest filed in U.S. District Court in Louisville, Kentucky.

Those instructions included orders to write to an e-mail address and wait for details on handing over an unspecified amount of money.

Pulver spent nearly 10 agonizing hours in her bedroom as the authorities tested the box to make sure it would not explode before removing it from her neck.

At the same time, the authorities say, Peters was stopping off in his four-wheel-drive Range Rover at a library and video store to check the e-mail account he had given Pulver and whiling away at least part of the time at a liquor store browsing for wine.

Peters, who worked in investment banking and law, on Thursday pleaded guilty to one count of aggravated breaking and entering and committing a serious indictable offense, a representative of the New South Wales Courts Service Center said. He will be sentenced later this month.

Investigators in Australia and the United States say they linked Peters to the e-mail address using video surveillance and access logs, and found credit card records showing that he had purchased a thumb drive, lanyard and baseball bat identical to those used in the extortion attempt, according to the complaint.

The document says he sauntered into Pulver’s room on August 3, wearing a business shirt, slacks and a blue, yellow and white mask that covered everything but his mouth and a pair of “saggy and wrinkly” eyes. He was carrying a backpack and a black aluminum baseball bat.

He said he wasn’t going to hurt her, then forced a black box around her neck using something like a bike chain and locked it, the complaint said. He attached a lanyard with a green thumb drive and a plastic document sleeve containing a note.

“Count to 200,” he said, according to the complaint. “I’ll be back.”

Pulver waited a few minutes, called out to him but got no response. She contacted her parents and asked for the police. After nearly 10 hours, tests concluded that the device was not a bomb.

Peters is a globe-trotting investment banker who went to primary school in Hong Kong, attended college in Sydney, ran investments in Malaysia and spent time in the United States, where his ex-wife and three school-age children live, according to authorities and his attorney.