An Australian investment banker pleaded guilty Thursday to chaining a fake bomb to a young woman's neck in a bizarre extortion attempt last year.

Paul Douglas Peters' lawyer Kathy Crittenden pleaded guilty on his behalf in a Sydney courtroom to a charge of aggravated break and enter and committing a serious indictable offense by knowingly detaining 18-year-old Madeleine Pulver.

Pulver was alone studying in her family's Sydney mansion Aug. 3 when the 50-year-old Peters, wearing a ski mask and wielding a baseball bat, tethered a bomb-like device around her neck. It took bomb squad police 10 hours to remove it, but it contained no explosives and Pulver was not injured.

The man left behind a note demanding money, along with an email address. New South Wales state police have said surveillance footage showed Peters in several locations where they believe he accessed the email account.

Peters, who traveled frequently between the United States and Australia on business, fled to the U.S. and was arrested at his former wife's home in Louisville, Kentucky, almost two weeks after the crime. He was extradited in September to Australia, where he has remained in custody.

Peters appeared in court by video from prison Thursday. He showed no reaction when his lawyer entered the guilty plea.

"Mr. Peters deeply regrets and is profoundly sorry for the impact that this incident has had on Ms. Pulver and her family," Crittenden told The Associated Press after the hearing. She declined to comment further.

Why Peters targeted Pulver is unclear. U.S. federal court documents show Peters once worked for a company with links to her family, but the Pulvers have repeatedly said they don't know him.

Pulver, who has graduated from high school since the attack, and her parents were in court to hear the plea. Her father, Bill, thanked police, prosecutors and members of the public for their support, and said the attack remains as mysterious and as "random to us in our minds as it did back on Aug. 3."

"There was no -- nothing other than just the fact of Maddie was in the wrong place at the wrong time," Bill Pulver said outside court.

"A poor decision by one man has prompted a truly extraordinary and inspiring response from many thousands of people and we will be forever grateful."

Bill Pulver was once the president and CEO of NetRankings, a pioneer in tracking online exposure and readership for companies advertising on the Internet. He left after the firm was sold to ratings giant Nielsen in 2007. He is now CEO of Appen Butler Hill, a company that provides language and voice-recognition software and services.

Peters will appear in court next on March 16 for a pre-sentencing hearing. He faces a potential maximum sentence of 20 years in prison.